My girlfriend wants an e-bike
Hi carbonazza, don't invest into LiPo technology and definitely not into Hobbykings own brand batteries. They are cheap with good stats on paper, but that's about it.
Why not Lipo: they are not durable, have short life span (low amount of charging cycles - at best 500) and have to be charged very carefully not to over voltage them with very expensive charger - else their life span drops rapidly.
What to get as powersource - LiFePo: best power to weight ratio (but not as good capacity to weight ratio as LiPo), very good durability - can be overcharged, under depleted, 1000 charging cycles with almost no capacity loss during cell's life, can be charged with cheap chinese chargers so that makes up for their higher price compared to LiPo.
Why not no-brand batteries (Hobbyking, etc): Batteries are made with different grades and are sorted as they leave the factory. The grade is usually determined by the internal resistance of the cell. Low grade cells loose capacity faster, reach less charging cycles, can get puffy easier and they get hotter drawing current from them. These cells usually end up in cheap LiPo packs.
I have very good experience with A123 LiFePo cells. They have also multiple grades, get the A grade as directly from the factory as you can. The longer the battery sits in warehouse the worst it is (some batteries can be old as 2 years then sold cheaper). Make sure all cells in the battery pack are the same age (so the whole pack ages the same and all cells have same properties). Have the cells professionally be welded together (not soldered but welded - some HobbyKing packs are soldered). This way you can have a pack much cheaper than buying it already made.
Now about the voltages and power:
E-bikes are powered by brushless DC motors. The torque of the motor is determined by the current flowing through, the max rpm is kv * Volts. Kv is a constant specific to each motor. So voltage influences the max reachable speed.
If your pack is connected in series then raising the voltage will not raise the current the pack is able to give.
Each motor has a limit how much current it can handle - else it will get burned. Adding additional cooling to the motor does increase the maximum torque it is capable of (granted the batteries can supply the current needed).
Looks like the Cyclone 3000 uses this motor controller:
http://www.ebikes.ca/c-phaserunner.html. It is able to handle 90V max and 40A max current with a 96A peak. These controllers have programmable limits and they have to be paired to the motor with PC (each motor requires different parameters to run smoothly). Maybe there are lower current limits programmed in not to overload the Cyclone 3000 motor.
It is also worth noting that supplying too much current for higher torque can damage the transmission even if the motor can handle it. The transmission has plastic wheels inside:
https://endless-sphere.com/forums/viewtopic.php?p=1054349#p1054349.
Increasing the voltage will increase the max speed and the power, but not the torque. The max power happens at half the max rpm:
http://motors.vex.com/introduction/.
