I have both motors, but my B5 is not fully broken in. The B7 is a steal @ 155, id take that not matter what. Its a great motor and im getting 9min if push on a tank. The B5 is probably going to get better milage, even now when breaking it in, it runs for evere even at the rich settings. The B5 will have a little more low end and it push my truggy from what can tell so far. Like i siad its still new so im running rich and slow.