I run 275's on my '98 Cobra's (17x8), no fitment issues at all:
I only wish they looked fatter though. For some reason they look much wider on a 9" rim. However, the difference in traction from going from a 245 to a 275 is like night and day, well worth it
but people say you wont get the full benefits if you dont use the right size rim is what i heard. i have 98 cobra rims and i think i wanna try some 275s next too but not sure if i should not waist my time