Fitting everything under the seat would certainly be a valid reason to go with a lower voltage pack.
The main problem I see with such a short pack string is the motor controller will low-voltage cutout at 70 volts. With only 22 cells, that’s only down to 3.18 volts per cell. With the voltage sag under load, the motor controller will cut out a bit earlier than this and cut usable pack capacity even further.
The motor controller has a high voltage cutout at 86 volts, which is how I selected 25 cells. 86 / 25 cells is 3.44 volts per cell; just above the full resting voltage of a LiFePO4 cell. I stop charging when the pack is about 85.5-86 volts. Even if I charged to 87.5 volts immediately tried to turn it on and drive, I would only have to run the lights a few seconds to bleed off that top bit of over-voltage and get going.
PS: For some reason, I stopped receiving subscription notifications to my original http://www.electricforum.com/cars/gem-cars-nevs-forum/3005-new-gem-owner-converting-lithium-batteries.html thread, so I didn’t notice new replies.
I’m planning on recreating and updated thread with all the original info I had posted updated with any new info and advice I have. I’d also like to make is a bit more step-by-step, to make it easier to duplicate my efforts for those interested.