Dude, M4. I already mentioned that and even put a pic of my bike with that pipe on it!
A pipe isn't going to make any difference with mileage. In fact, it might hurt the mileage a bit if anything. I averaged around 45 romping on it. That was the worst I could do in city riding. Out in the mountains and canyons I'd typically get closer to 50mpg.
I'd like to get a black one, that silver looks weird on it!
Any advice on integrating the blinkers in the rear, and shortening the fronts?