Kepler raises some valid points there. If you intend on pedalling, a single speed setup will hamper you bigtime.
Even with 5kw at my disposal, i still pedal alot to help with range and also to help take some load off the motor after i've heated it up with some hard riding and the ability to do that at either 10kmh or 40kph is handy - something a single speed setup can't achieve.
For off road riding, the HT's wheelie popping ability is great for lofting the front end over trail obstacles, to the point where i've almost looped the bike out from giving it too much juice at times (26" rim)
Thats on 20s lipo, i've heard from other people that they have even more mid-range pull on 24s lipo
The Mac motors are a good unit, my girlfriend uses an 8t rear motor in a 24" rim and loves it. Its mild at lower wattage but moves along nicely at 1500 - 2000w. However as Kepler mentioned, reliability can be compromised at this power level, to the point where i ordered a spare clutch for ours incase the original fails due to the power being used. Heat can also be an issue at this power level. But if pegged to say 1000w max however, it would probably be bullet proof