another quick tire clearence question

In a drag radial, or all out slick it wouldn't be so bad because of the soft sidewall, but for a full on radial street tire, I wouldn't bother. The problem is, is that it needs to be over inflated in order to maintain a constant contact patch on the road, because they tend to "bow" in the centre because the rim is trying to keep the tire as tightly fit as possible, forcing the edges together. Over inflating it helps to overcome the bowing effect, because it forces the center of the tire out, but then you've just hardened up the tire all the way around, to the point where it will now no longer flex in the sidewall, causing traction issues again.

From a handling standpoint, you've now got more sidewall to contend with, which causes the rim to "sway" back and forth inside the tire under hard cornering.

I wouldn't go any wider than a 255 for a street tire on a 17x8" rim, were I you. You’ll gain no handling advantage (and in some cases create a disadvantage) and you’re also increasing the rolling resistance and rotational weight of the wheel.