So what's the actual difference between the 48v and 60v motors? I've put 70v through my 48v motor without any issues. Also, the 48v motor with a shunt modded 48v controller pulls 50 amps and moves my 300lbs or me and kart up hills with ease.
Effeciency
I put ~40V thru a 24V 450W motor
http://www.diygokarts.com/vb/showthread.php?t=36894
I also did some testing "straight" off of the battery pack
http://www.diygokarts.com/vb/showthread.php?t=39287
* "Personal Analysis, of the (3) tests with the ZY1020 48V 1,000W motor
Alfa Wheels speed controller
Take-off ~25A
Accelerating ~25A
Constant/crusin' ~12A
Top speed ~14 MPH
TD Pro speed controller
Take-off ~30A
Accelerating ~30A
Constant/crisin ~10A
Top speed ~14 MPH
With-out a speed controller (just a battery pack, beefy switch & motor)
Take-off (up to) ~100A
Accelerating ~50A
Constant/crusin ~10A - 12A
Top speed ~14 MPH
So, (as Sid said) the speed controller (available amps) doesn't seem to be holding the motor back
The only advantage, I see, is a "harder" acceleration
...but, at the expense of "lots" of amps
…& the top speed was still ~14MPH either way"