Should I have said an asian and a caucasian? As I said, the races in TES are more cultural distinctions (i.e. nationalities) than they are biological ones. There are Khajiit who look just like humans, and Khajiit who look just like housecats. Both types can theoretically mate with Imperials. The Imperials are really a catch-all term for at least 2 (but morel like 22) different peoples. Since we can now choose how fat or skinny we can be, does it make sense that a fat Khajiit can outrun an athletic Breton? Not to me it doesn't.
You cant tell anyone what the races in this game are supposed to be separated by unless you are on the dev team. With that said, the fact that Khajiit have different physical traits and can resemble humans is irrelevant. The fact that that they can mate with humans is also irrelevant. Even in real life Kenyans are known to be amazing long distance runners due to their body structure and elevated environment. No one disputes this. It is evidenced in their success in marathons and if I recall correctly they too can reproduce with Europeans. Ask Obama's pap. Sure we can play the PC stuff or name exceptions but what is the point of homogenizing everything to the point where nothing will matter in a few levels?
People are just asking for a good reason to pick an athletic type of character. What is the use of playing a Redguard who is supposed to be known for "quickness of foot" when in the end he will get no real benefit from this intrinsic value? What the point of playing a Nord or an Orc if a Bosmer can still lift just as much as he? Might as well pick a Breton or Altmer because no matter what their magic will truly be superior. Might as well pick a Khajiit or Argonian because at least their traits are truly helpful.
If you want to create a somewhat athletic Breton, then you can. I even advocate the ability to increase his speed based on perks and whatnot. But no... he should not be faster than a khajiit for no damn reason. Its a cat for Christ sake.