Is there a suspension system you can buy, Pedders or some others, that will allow you to put wider tires on the back without cutting or rolling the fenders?
My dream would be a pair of 315/30's on 18's.

I may be incorrect but a good stock height increased spring rate rear spring with drag bags and you should be able to get away with a 275 in the back. I'd give Pedders a call or contact them via e-mail and see what they may recommend. Not sure if we have anyone on the board running wider rears without rolling the fenders though.