I am the tire professional, lol.(unfortunately) Stick with whats recommended 255/45/18. Sure the 275 would fit, but their ain't jack sh*t in that size, and its a larger diameter than stock.

 

The diameter is only about .5 more than stock. This should fill out the wheel well better without being noticeably taller. There are actually quite a few tires at www.onlinetires.com in that size. Oh well....it will be a looooong time before I'll need tires anyway.