I'm not a big fan of race penalties, but at my table there will always be race bonuses. That said, of all the abilities, the only ability score that ever comes up as "unrealistic" is Strength. No one gawks at a genius goblin or a charismatic dwarf.

I've also never liked caps for most abilities for PCs, monsters certainly don't have them. But it seems sensible to cap Strength based on size, not race.

So, my house rule is a cap of 20 for medium, and a cap of 13 for small (originally, I had it at 12, but multiclassing requires 13), and a cap of 26 for large or medium with powerful build.

I suppose a small race with powerful build would have to be higher, say 19. I don't know of one, but there could be.

I have no caps for any of the other scores based on race or size.