For an FD a slower turning motor is better as it will drive a larger roller(if direct drive). Leaving the motor governed will get around 22/25mph with a roller in the 2" range depending on where the gov. is set, usually around 3600rpm. Ungoverned will of course be faster. The 2.5 lifan will easily turn into the mid 4k range. Would expect the same or better(being OHV) from the Honda. I had one Lifan powered FD that I ran a 3.5" roller on. Would exceed 40pmh, but you had to pedal it pretty fast to engage the drive due to the high gearing. Was a much more pleasant ride with a smaller roller and a 33mph top end. Cool thing about a well designed DD FD is ratio/speed changes are as easy as a roller change.