I don't think you'll get much more than 77-80mph on this quad based on it's tranny...it really isnt geared for more than that...I don't like the top speed debate but im running the big 3, kx cams & 15/37 gearing and do about 78 ...(based on gps reading)
I have the FuelATV intake, pciii & exhaust (dasa).... think I paid around 250ish for the kx cams and another 200 for the dyno..for me it's worth every penny!
with that gearing think you be better on 8" rims and 18" tires same gearing I run on my mx yfz