Just installed an MPI Supercharger kit on my XTX and have to say its wonderful. I'm running 5.5psi boost at the moment (185hp) on straight 92 octane pump gas while I'm working on getting the primary clutch dialed in. I also found a good deal on EBAY, got the 180hp Mountain kit for $2,200.00 including shipping.
Took me about 30 hours to install it, very nice instructions and a very nice quality product that has been on the market for years and is proven.