Sorry, forgot about getting back to you on this. I've got two main motor assisted bikes that I use for commuting almost all the time out of my fleet that are right in that speed range notch and are "commuterized" MTB set-ups as I explained. On is a gas motor assisted bike and one is electric.

For the gas this is what I'm using with a 60t-11t gearing (consistently gets about 150 miles per gallon): http://www.staton-inc.com/store/prod...it-389-14.html

The electric is a little more complicated and I didn't just use a kit as is. I did pick up the "guts" of a GNG brushless mid-drive. The one they are selling as a 450watt model but controller and motor is actually rated for 20A at 48V. Bought it off of a guy who didn't like it because it kept chewing up belts all the time and he broke the wimpy freewheeling crank set that comes with that kit. We haggled over price and he sent me what was left of the kit for $150 shipped including the broken crank parts but with no battery and a chewed up belt (kit is $400 new plus shipping). I then used a dremel on the motor side belt pulley and smoothed the sharp edges which are part of what makes them eat belts and put on a new belt and then ran it off of a 36V 15A old Crystallite hub motor controller I had laying around. This puts a lot less stress on the belt and also reduces the motor speed by about 25% so that it more closely matches pedal speed on the crank and it isn't trying to spin the crank so fast that you can't pedal fast enough to keep up and help out with your human power input. All these modifications based on the experience of others posted on the endless-sphere forum about this kit. I am powering it off of twelve LFP-G20 cells in series (LiFePO4 Screw Top Terminal Prismatic Cells, 3.2V, 20Ah, 10C, 1.65lbs) separated into three sets of four cells to allow 12V parallel charging and 36V series output. I then used freewheeling crank components purchased from both Sick Bike Parts (.com) and Staton-Inc (.com) to build a much better stronger freewheeling crank using their heavy duty parts and mounting double big chain-rings on it. Outboard chain-ring runs forward with a short chain to the mid-drive motor kit mounted just forward of the bottom bracket on the down-tube and the inboard chain-ring runs back to an 8-speed free-hub cluster with a 12t,13t,14t,15t,16t,20t,26t,34t set of sprockets in the rear (custom layout pieced together). I usually pull away from a dead stop in second gear (save first gear as a granny gear only for BIG hills when loaded down with cargo) and only have to shift twice to be in my high range for travel speed on the flat and all the gears after that are single tooth difference to trim my gearing for conditions usually cruising in seventh or eighth gear on the flat pedaling at about 90-RPM pedal cadence with the motor and my pedaling running smoothly together.

I've got other electric and gas set-ups that run a little faster or slower but in every case I've got them set-up so that my pedaling and the motor work together. Most are mid-drives that run the power of the motor through the gears of the bike but I do have one hub-motor bike (my fastest bike that will do 28mph under motor power alone and go over 30mph with pedaling but short range and heavy with its 1.4Kw "Brute" rear hub motor) and I've got a total of two of the Staton-Inc axle mount kits which are single gear ratio for the motor. There is also my bike with just the hill helper motor which is a cheap junk 200-250 watt hub-motor outside of a wheel that drives the rear wheel through a 2.125 gearing reduction so it is only good for help to climb hills and on the flat you can go faster then the motor can spin just by pedaling. All the rest of my motor assisted bikes both electric and gas (and one that is both) put the motors power through the bikes gears for multiple drive ratios matching the motors RPM to the pedal RPM so they work together in unison. Wheel RPM has a much wider "sweet spot" range then pedal RPM so if you match the motor up to the pedals instead of the wheel and take advantage of the bikes gears it makes for a much better build in my opinion. But then it is all about what your looking for to begin with.