go with a little wider tires, the 255's will kinda pull in. i have 275's all the way around & they work just fine, aside from the occasional tracking on not so good roads
255's arent bad on the front but don't you want something a little meatier in the back? 265/35/18's seem to be the best compromise. I've had a 275 series Kumho rub on in the drivers side front on fully locked right turns. This led to (or was caused by) a bubble formation/seperation on the inside face of the tire. I've been through many sets of Kumho's in the past (this is my 3rd '99 Stang!) but I've finally got disgusted with how quickly they wear. This time around I went with Pirelli P7000's because they were relatively inexpensive at $180/each installed, after tax. And while they are reportedly not particularly outstanding in any one category (i.e. tread life, wet/dry traction, noise), they also aren't particularly bad in any of those categories either, according to reviews I've read. Every tire is a balance of compromises. I just got 'em 2 days ago and they seem sticky enough but l'll be watching how they do.