Sometime back, I did a
"Turbo Button" for the Electro-Metro back when it was running on 72V.
The idea was to increase system voltage for a higher top speed than the PWM controller I could afford would support.
Ryland, it sounds like you want to bypass for increasing current, rather than increasing voltage.
At almost any voltage, 500 amps is a respectable amount of power. You only ever pull peak amperage during really hard acceleration or big hill climbs (or really bad gearing!)
It always seems like the point of good electric car design is to MINIMIZE current, except when you really want some OOOMF! An 11 inch motor by default doesn't draw some tremendously greater amount of current than, say, a 9" would.
I think the easy answer would be just to put a 500 amp controller in the car, and try taking it for a few drives. If you really aren't happy with it, go with a 1000 amp. At some point, the batteries will be the limiting factor!