You might check out Rad Power Bikes with PAS 0-5 and throttle. The twist throttle has an on/off button and the full 750w of power is available in any PAS level when using the throttle (even at PAS 0). Very nice feature for getting across intersections in a hurry, short inclines, pushing the bike up inclines, riding over obstacles that would contact the pedals if you only has PAS, etc...
Some of us added a thumb throttle on top of the twist. I find it easier to twist in the right amount of power and have better control of the grips on rough terrain with the thumb throttle attachment.