its actually the motors being in parallel im refering to Jamie, not the batts.

If you are running 4 motors, Im assuming you have 2 on each speed controller, meaning only 2 controllers needed.

If you wire both left side motors correctly, (for example), to one electronize controller, one or 2 things can happen.

you can connect the motors in series, meaning the 2 motors share the 14.4v under normal running, giving 7.2v each. (this is not always the case, as one wheel may spin for example, then the spinning wheel gets move voltage). Under normal running, this method means the robot runs at a speed that suggests it has only 7.2v of batts on board.

or.... you can connect the 2 motors in parallel, giving 14.4v per motor. The robot runs twice as fast as if wired in series, and has more power, but current is also much higher so be careful.

if you have wired in parallel, run the motors at 150% voltage, setup the controllers right, and charged your batts, the only other ways to get more speed are to...

a) bigger wheels as suggested above
b) pull one stage of gears out of the gearbox
c) remove the ferrite rings on the motor.

all of which reduce pushing power and acceleration.

hope this clears it up.