i believe a big factor is the sand, the sand out where i ride 21" 8 paddles grab well for my ltr that is similar to your hp range.   soft coarse sand provides good surface for the tires to grip. those other tires however your hpr motor would have destroyed them IMO. my stock top end tri z runs those and they work well for 250 motor. are you going to be racing on a flat straight or up hill?
i will say play with the air pressure on your paddles. i first try a few launches with about 2psi and see if i can launch hard but not have to let off the throttle bc i wheelie out of control. if that happens then i go to about 3.5psi and that seems take some of the initial bite out of the launch. that is for a short run race. if its going to be a long race >100meters ill just run them at a higher psi bc to much bite will slow you down the longer the race is.
 the 3 "L's"  of drag racing, longer, lower, lighter   
good luck in your race, get pics and make the quadracer community proud