I think your top speed is most likely hampered by the clutch kit. You said you bought the quad with these modds already on it. Jetting is a possability but I bet with a list of modds like that the quad had some aftermarket tires and wheels on it at one time. If that was the case and they were oversized like many guy's use, the clutch kit could be one that was to aid in the use of the oversized tires and now that the machine is back to stock size tires the top end is a little lacking. Its not off by much though. My P650 has similar modds and on pavement with the tires pumped up to about 15psi I have broke 70mph with the stock clutch setup. there is a simi stock 700 in our group that has a basic mono spring clutch kit from dalton that helps in the bottom end but drops the top speed by about 4-5 mph. It gets to 45 quicker now but looses steam quick after that. Prior to swapping out the primary spring it could hit 68 pretty easy on pavement.

sammydogs64, I think your added unsprung weight is eating all kinds of power. most 27" mud tires weigh at least 10 pounds each more than the stock tires. Depnding on the type of terain each of those unsprung pounsds can be equated to anywhere from 6 to 1 or as many as 9-1 spung vs unsprung weight. To put it in easy to understand terms its like riding with a 200-300 pound passenger. It will take an easy 20% of your power away.