Hey guys,
the capacitor comes into play only during switching, that is during partial throttle. Once your at full throttle it makes almost no difference whether you've got one or not! So for all you stock guys who use a lot of full throttle I doubt it would make much difference, but for mod guys who use more partial throttle it should make a difference.
If you use very large value capacitance it means that the voltage will drop less during turn-on time in partial throttle (thus giving more voltage for the motor and more punch), but during turn-off time it will also take longer for capacitor to charge up and thus the battery vcoltage will also rise back up slower.
Small capacitor -> during on-time voltage will drop more, but will also charge up quicker.
Large capacitor -> during on-time voltage will drop less, but it takes longer to charge it back up again, so the battery voltage might be kept lower because of this.
It's good to use a capacitor but don't over do it by using too large value capacitance.
Just keep these things in mind when choosing your capacitors.
Cheers.