I had 275/60 on a 15x8 with 4.25 rear space and they fit with no problems.
I've also had 295/50 on 15x8 with 4.75 rear space and they fit with no problems. The back side was a bit close to the spring, about 1/4", but I had plenty of room to the wheel opening lip.
I've had 295/65 on an 15x8 with 4.5 rear space. They fit and would work for drag strip passes where hte rear was lifting. Never had any mroe than my butt in the seat during those passes, but they looked like they might rub with some extra weight in the rear seat.
I should probably also mention that my wheel openings have the stock quarters and have had the edges rolled, so I've got almost 3/4" more room than some guys with restoration quarters and unmodified openings.