Hmmm, i would be happy with about 10 out of your 600. Perhaps a hair more. But sometimes less depending on how ya are on the throttle that day and powder conditions. So about ten.
Now who would win. If the xc was tuned right, it would at least be a tie. The thing the zr has is the EFI and thus the best mixture per temp. ALl things being equal though I would imagine about the same.
Yeah. the efi sled should take the xc just due to its proper mixture that is constant no matter what temp. I get better gas milage now with the VF3 than i did stock. friend has an xc600 and we used to be dead on with gas. now hes empty and im still somewhere between 1/8 and 1/4 depending on how we're riding.
only on hard pack and ice. Check out some information on clutch kits for your sled. Reeds would also help and a silencer would give you weight reduction AND performance. those are pretty much the cheapest engine mods that would give you a major advantage.
throw in a pipe from slp along with that silencer, loose 10 pounds and gain 10 hp. with all this a little clutching will be in order but slp has all the specs for ya. Those along with what maverick said will get you a little past the 120hp mark.