Suitable motor advice

[B4 Sloth]

Hey,

I am currently running a peak 13 double bought new off e bay. Has adjustable timing. Not as fast as i thought. Will advancing motor a bit make much difference. I am running a 21t pinion, my local shop did not have the 22 that the manual recomends. Would a 23t make much difference. Am i better off looking for a bargain on e bay...such as the Peak suritan 12 x2. Or a 12 single. Whats best to do?