great machines! I have a 99 ZR 500 that I absolutely love. I have just over 12,500 well maintained miles on mine and it is better now than ever. The pros, it will last as long as it is taken care of. Even though they have the ability to run MTBE and oxygenated gasoline, I would avoid it at all cost (have had several piston meltdowns due to that, Damn MN gaspumps). I do a top-end rebuild every 4,000 miles or so and plan on a complete chasis re-rivit and bottom-end rebuild after this year at 15,000. The top end speed is reletive to your gearing and clutching. I could easily hit triple digits with lake gears. I have since switched to climbing gears for a trip to the mountains. Powerwise these sleds are pretty hot from the factory so any additional gains may not be cost effective. Clutching is your best bang for the buck performancewise. Aftermarket Y-pipe, expansion chamber and resonator will drop a lot of weight and the addition of some reed valves help too. I have done all this and even though the manufactors say I should have gained 17 overall HP, I have only gained 12 and am currently at 108 HP @ 8500 RPMs when I put it on my dyno. If you ditch-bang at all, be sure and tighten your rear suspnsion bolts on your tunnel every so often or you may just tear out a coolent bar (that really sucks). The 121" inch track is good, but my riding style has changed and a tunnel and rail extension was worth the expense for me instead of purchasing a mountain sled. Now I have a 136" track. With the right tunning and effort, you can make you 500 into a sled that acts like a stock 700! Enjoy the ride and pray for snow