I havent heard anything bad about the 600's they don't handle as good as the 07 and ups but they are lighter than the 06 700 and 900's. They should have some venting done the keep the hot air under the hood to a minimum. I added the XXX Mod Rods side panel vents to myh 06 700 and they are awsome. I had an 04 XC 600 before my 06 700 it took me a little while to get used to the new chassis but I would not go back to the older chassis. You will gain reverse to I'll never get another sled without it.
i like mine so much, I sold my 07 rev 800 to get another. I now have 3 of them, one is stock with a pipe, one has a Union bay ported motor, and one is a turbo. The 600 engine spins so fast that it is instant hp. It is surprising how much they will climb with just a pipe and some clutching.
These are the easiest, most fun sleds I have ever rode.