For a street driven car, 275/40-17s on 17x8" wheels isn't a problem. They do hang over the lip a bit, but it isn't terrible. See the attached picture here. That's my car with 17x8" wheels and 275/40 Sumitomo tires on both ends. Now for a race (race with turns) car, having the tire hang over the wheel like that isn't really optimum because first, you aren't using all the tread, and second, the overhang makes for a little sloppier steering. I have driven my car on a road course with those wheels/tires and it isn't terrible, just either wider wheels or narrower tires would work better. I have another set of 17x9" wheels with 275/40s on them (Nitto NT01s) and they fit perfectly.
If I was buying a tire for competition, I wouldn't exceed 245s for an 8" wheel or 275 for a 9" wheel. For street it isn't matter near as much. 255s will fit with no problem, the only thing there is what ratio do you get? 45 or 40? One is slightly taller than stock, one is slightly shorter.
Anyway, the bottom line is you can run any of those sizes on 8" wheels. Sorry for the long winded post, I hope it helps you out. Oh, and this calculator is handy: Tire dimension calculator