diirk's RR was an '05 800 EFI, he subsequently had the engine ported and polished, went with a single exhaust with custom muffler, cold air intake, added a Power Commander, and installed a Heel Clicker clutch kit. He eventually sold it for a Rhino for the extra cockpit room. At the time it was touted as the fastest RR.
The 800's ARE better than the 700's in the dunes.
One solution that I heard about to alleviate over heated and broken belts while duning was to disconnect the EBS.