I've been looking into this matter for a long time myself, and I came to conclusion that 20x9 will be the best solution due to the fact that 275 will be the widest you can fit without modifying the fender in the front, therefore, there odd no point of going with a wider wheel as it just creates more mass. The offset, I'm still figuring out, but I think that 35 to 38 mm should be adequate enough, with 35mm being more favourite.