I went with the Dial-a-Jet over a jet kit, for its ability to be adjusted outside of the carb.
I take a couple trips a year to WV and with 15 minutes of time I can adjust for altitude or temperature. It works great and I have had 0 issues with it in 4 years. Check out its website before you pull your carb apart.
I also installed a spark plug capacitor from Direct Hits. I had an immediate improvement in throttle response and picked up a few MPH on my top end.
I also have an HMF exhaust, K&N filter, and clutch kit. I have ridden my Vinson thruough 3' deep water, in mud, snow, various altitudes, no problems. In WV my ATV topped out at 60mph with 27" tires. I thought that was pretty good. In comparison my stock '05 Kingquad 700, with 26" tires topped out at 64mph.