If you are sticking with a low profile street tire, it's all about width. I don't think any of them have enough give in the sidewall to really help you out much with traction, so it comes down to how wide you can get your tire.
If you are thinking about drag racing and fitting a "real" flexible street drag radial like a Mickey Thompson, then sidewall height becomes a huge factor IMO. The taller the radial you can put out back, the better off you are traction wise. Running these has some trade-offs in the real-world street driving, so you might be better off having a set of drag wheels/tires. I have a pair of 16x8"s for some decently tall M/T radials on the Supra. I don't know if they make anything decent sized in 17".
As far as the amount of fender flare you want to put in, I can't give you an experienced answer, but I can guess a bit.
I run 295/35/18 on a 18x9.5" wheel with a +22 offset and they are seriously poking out.(I would be way better off with a +35ish offset, but this is a special offset set I had for my old 240sx. I am looking into maybe getting these wheels machined a bit to help me out.) Even with the perfect offset of the wheels where they were just barely off suspension, I would probably be at a "perfect" fit. (Perfect with the fender rolled, anyway)
So I'm thinking you need at LEAST an inch and a half of flare out and some perfect offset to pull off 315's on a 12" wide rim. That's a wide-ass wheel.
Don't take all of this as perfect facts, I'm just doing this off of memory and the top of my head.
I want to flare my fenders also when I get into my bodywork, let us know how you did it and how it went.
---------- Post added at 02:49 PM ---------- Previous post was at 02:44 PM ----------
And speaking of 750hp, you've got no chance of putting anything near that down until you are already moving, you are on the right track figuring out how to get as much rubber back there as possible. If I were you, I would be running a drag radial all the time and be very careful. I see you are in Maine, fun.
I had probably 350whp-ish this summer, and I was smoking the 295/35's in 1st and sometimes through second on a hard 1-2 shift. I don't have any stupid camber like some people either, the tires are all on the ground.
