The Ford Y2K rims are 9.5", and I have 275's in the rear and will go to 285's in the Potenza SO-3's (great tire btw). I have seen 295 Goodrich KD's on this rim and it didn't look odd or that it was buldging too much.
I wish there was a 10-10.5" version of this rim so I could get 315's, I wouldn't be able to run the SO-3's but I'm sure I could find another tire.