We went up to 18's with 225/45's from stock steelies--mileage reads absolutely identical, which means it really got about 3% better. I was also surprised that it really didn't drag the car down either. Much as i intended to stay at 17 or less, we're really happy at 18".
Cool. I think those will look good with your blue. Post up some pictures when you get them on. I went with 16" also, for multiple reasons. I like the look of 18s, but the potholes around here are terrible, and I was afraid I would screw them up in a hurry. I use my car as a daily driver, so I thought the little bit more tire flex would help smooth out the ride. It also didn't hurt that I got to keep the stock tires, and that when I do need to replace them, they are significantly cheaper. I am happy with mine, I hope you enjoy yours also!