((My own thoughts and notes about the Khajiit breeds, generated by speculation and my own head canon. I put it here as it's not likely to find a place to be used in TR, but comments are certainly welcome!))
EDIT: Some of this is outdated as I research lore or correct logical inconsistencies. For most up-to-date lore, see latest posts.
A rare breed, as they are typically born only one at a time. Elephant-size (Indian), quadruped, the forelegs slightly longer than the hind, similar to a hyena.
In war, they fill the niche of elephants. Though Khajiit warfare tends to be guerilla, it's assumed they could pull siege engines or supply wagons if it was needed, and some Imperial or Dunmer outposts may have tried to contract out or enslave Senche-Raht for this purpose. Among Khajiit, instead they are like large mobile platforms either for the bipedal Khajiit to shoot arrows and spells from, or the smaller Dagi and Alfiq breeds to leap down from in hordes to claw at the enemy's heads and eyes.
Domestically, Senche Raht are often where there is heavy manual labor to do, such as construction work, farming, quarrying, or hauling wagons. They are less fierce than they look, the term "gentle giant" may apply, and are sometimes also tasked with such things as looking after Khajiit children, particularly as they age and lose their strength. They will sometimes also look after livestock, particularly the more dangerous creatures such as bulls, as they are big enough to be able to control the beasts but gentle enough to not abuse them.
They often have a fear of boats, not because they can't swim, but because the barge that can house them comfortably has not yet been made!
Particularly grand parades or travelling circuses may use a senche as a centerpiece, decked out in colorful ribbons and with bipedal Khajiit peforming acrobats along their backs.
Birthing a Senche-Raht is considered a great honor. Gifts of gold, moon sugar, high quality meats, and medicines are common to give to such mothers; though this has become a ritualized affair now, in earlier times it probably developed as an aid to keep the mother healthy through her ordeal.
Often born in litters of 2-3. Horse-sized, forelegs twice as long as the hind, giving them a somewhat ape-ish posture.
In war, they are most often used as cavalry or supply carriers, filling in the niche of horses or donkeys. They are comparable to the Pahmar-Raht in this regard, but can carry more and are somewhat less manueverable than their smaller cousins. They are also slower than horses but can leap further and climb cliff faces and some castle walls. Senche are also able to walk on their hind feet for short distances, like a gorilla, and their forepaws have longer toes and a vestigal thumb that allows them to pick up and throw objects, but typically not use these objects with any skill.
Often quite loyal to a "blood-brother" or "blood-sister" who is also their rider; though sentient, they tend not to think for themselves, in the manner of a beast following orders, preferring to let other Khajiit take care of more complicated clerical tasks. Some Khajiit consider them stupid for this reason. They are little more clannish to their own stock as a result, choosing one Khajiit of the other stocks to pair with as a rider, or mingling solely with other Senche. This is the main reason they are not common outside of Elsweyr, and outsiders are sometimes confused by the term usage (aka, the ESO retcon).
Domestically, Senche will sometimes perform as scout or courier mounts across deserts and difficult terrain, as they have more stamina and climbing ability than the Pahmar-Raht, and can take care of basic tasks requiring hands should their rider become injured or die. They are not as fast and graceful as the Pahmar-Raht however, and so are often not used in situations where mounts are for show (parades, mounts of the nobility, etc). Besides living in their own clans, Senche may also be encountered alone, filling in the role of ranger in other genres. Being bestial they are more in tune with nature, but also have just enough smarts and hands to care for it. Senche may struggle with walking the fine line between beast and human.
Often born in litters of 2-4. Large as a horse, quadruped. "Giant tigers".
In war, Pahmar-Raht are used as mounts or shock troops. When sprinting, their speed may match that of horses, with claws and teeth to boot. Riding one takes skill however, as they are more instinctual and bloodthirsty than Senche, and liable to run off in their own direction rather than follow the command of their riders. Some armies don't even bother putting riders on them and instead just send them in as their own unit for this reason. Also, as they have a long flexible back, they are also harder to "seat", and require special saddles that force the rider to lie flat and hold on with their hands.
Domestically, they make good guardsmen, fishers, and hunters. Because they have no thumbs, they often have to hire bipedal Khajiit to handle their money, craft clothes and tools, do the cooking, and keep the books for them. Many Pahmar-Raht choose not to live the city-life for this reason, instead living almost half-wild on the edges of the wilderness, killing prey like a beast. Many a "Senche-Tiger" encountered by an outlander might be a Pahmar-Raht instead, either succumbed to hunger or disdaining of revealing its true intelligence to the foreign intruder.
Pahmar-Raht are also sometimes used as couriers, with or without a rider, as they are swift runners and can tackle most rough-terrain with ease.
Personality wise, they tend towards impulsive and aggressive, with the confidence to back it up. They are ravenous as kits, as they do much of their growth to full-size in the first 10 years. Though at their full height as teens/pre-teens, they are also rangy and at half-strength still, with the possibility of being injured if they try to take on an adult workload. In some Khajiit towns with a large population of Pahmar-Raht, it is illegal to employ them in manual labor until they reach the age of majority.
Often born in litters of 3-6. Quadruped. "Smart leopards".
In war, Pahmar are used like wardogs. They may accompany a bipedal Khajiit as their backup, for special assignments, or let loose in large groups to speed across a plain and soften up the enemy. They are too small to be mounted by any Khajiit except the smallest Tojay and the Dagi, who sometimes prefer them to the "large stupid Senches". Pahmar are easier to control than the Pahmar-Raht, but no less difficult to ride.
Pahmar are somewhat calmer and clearer headed than the Pahmar-Raht, and have a taste for refinement, taking pride in their comparative grace. Females may opt to become part of an aristocrat's harem so long as they can wear gold collars and diamond tipped claws, for instance. A Pahmar's physical development also differs from Pahmar-Raht, being almost the opposite: they grow only slowly until the rapid teenage growth spurts. They are typically not as fixated on food in childhood for this reason, taking the time to develop their agility and dexterity instead. Their adolescence is then marked with persistent hunger and impulsitivity (think human teenage boys), and it's common for a mother to scold Pahmar teens by telling them they're behaving like "the 'Rahts" and that they need to "act their size".
Domestically, they serve in the same role as do many big dogs of other races--for herding, hunting, guarding, pulling light carts (pleasure or work-related), or companionship. Though they do not have the scenting capabilities as strong as dogs, they take pride in their sensitivity to the subtle, and are often found in the shops of perfume-makers, alchemists, or gourmet cooks, aiding them by telling them if their recipes smell right. They might also help track down and catch criminals, and enjoy being bounty hunters, as this fills their animalistic hunter urge. Being used as a companion may also sometimes mean being used as a prostitute, particularly for Pahmar with a skooma problem.
Like the Pahmar-Raht, many outlanders mistake them for being Senche-Tigers. Pahmar are smug about this, happily playing along and milking the outlander's stupidity for all it is worth.