Leave it stock and take your money and put it towards better suspension, tracks, etc. If you're only riding the mtns. 2-3 times a year, this is not going to give you the time needed to properly set-up and tune a bigbore or turbo. These bigbores are not tow and go. As for the SLP kit, it helps and would be the most that I'd do in your case, but the horsepower rating is a little high imo. If anybody was to get my money in the states, it would only be Bigjohn!
It hasn't been a very good year for RKT. A good businessman should be taking and returning customers phone calls rather than arguing with competitors on dootalk. But that's just my opinion.