No one on this thread is talking about setting up wheels/tires for a SCCA car. If all out handling is your deal, go to the size rim in the middle of the range for the tire to achieve the best performance. If you can tell a difference in a 1/2" wide wheel then you are probably a professional race driver. After a 255 in a street tread like BFG T/A's, it's all for looks, not gription.
I was actually running 275/50R15.
Real tire shops have no issues, Wal-Mart or the other chain stores ran by lawyers barely will mount anything except what came stock, from what I've heard, I don't go to those types of shops.