Shouldn't have any tire rubbing issues. I'm running 275's all way round but I rub with my H&R's on 9" rims at full lock. It's the rim rubbing against the sway bar.
Shouldn't have any rubbing problems, My Eibachs have my Cobra sitting bout 2 and 1/2 inchs lower the stock ride height and have rubbing problems with 255/45/17 up front, I mean my Cobra is on the ground almost, but that will change when the H&R race springs go on today or tomorrow! But you shouldn't have rubbing problems cuz i have had 275/40/17 on my other 96GT and that thing was just as low as my Cobra so you are not going to have problems I don't think!
KEVIN
some of it depends on the offset of the wheel. On a 9" rim, you'd ideally want anywhere from +24mm to +28mm. On 275 40's within this range I do not foresee a problem.
Just spoke with a friend who was looking into 19x9 fronts and 19x11 rear. not sure what springs he has, but he thinks they should clear. I have seen a 95 Cobra with 19x9.5 front 19x11 rear with H&R race springs. Never heard it rub, but he has very low profile tires. Kevin