A lot of variables but if it was me I would try to set the rear as soft as possible without un controlled wheelies. Keep softening till that happens and then stiffen up a tad. Zero toe in or toe out both front and rear is the fastest but may also be harder to drive in a straight line. Try to run with a half tank or less of fuel, unless this presents tuning problems. 4 aa batteries instead of a hump pack and set a wing to neutral or take it off to reduce wind resistance. Any reduction in weight and resistance, check your bearings also, equals more speed. Good luck.