255 is absolute max on a 8.5, I am running a 9 with 255/25 and its square, no issues with tc system (235 front)
Is It worth it, depends a lot on what you use the car for and whether your happy with the look of the Rays. Most on here upgrade to 19's and run a 275, 245, buts thats for looks not for performance, lack of traction.