What are you trying to do road race it? Its my expereience that the 275 that comes on the stock rims are actually a little to wide and create a little more roll then I would like personally on a 9 wide rim. I've seen a couple 9.5 rims up front and to me this would be perfect for a 275.
You can't run much wider with our shit suspension setup, the contact patch won't increase and you'll just track all over the road. You will notice about zero performance improvement from a 275/285 to a 315