How big is too big...

The higher the side wall the more the tire will stretch. A 275-60-R15 would go on easier than a 275-50-R15. I don't even think it's possible to get a 275-50 on a 10 hole wheel. A 275-60 would be possible because it will stretch.
 
I just ordered the BFG Drag Radial 2's in 235/60/15. They should work out fine. I just needed something desperately.... with the horsepower i'm pushing, stock suspension, 3.73's, and street tires I wasn't getting any traction what so ever!

youll be surprised what a difference just the compound makes, width doesnt really matter much.