daromer: I agree it's not about speed. But, a 25% throttle motor will draw far less current than a 100% throttled motor. Hence, the reason why I said creeping up to speed, aka acceleration
Secondly I refer to feasible as in the size of the pack, nothing more. Using lower amp cells will require far more cells to accomplish the same task as high amp cells. Depending on fast and how far one wants to travel will determine the overall size of the pack. However, if it's only for testing a few 100 meters/ft, then the size doesn't really matter. But if they want to go 30 miles/km's at a decent speed, then pack size is very important.
That's why I said mixing them is fine, and is possible, but not really feasible for long usage, light weight, and high acceleration/speed. In the e-Vehicle arena, I'd want a battery pack that can deliver the highest amps possible with the smallest pack possible.