I haven't yet. I was going to get a set of triple rate elka's. I have heard these stock ones can be redone to equal that of the elka shocks so I might head down that road instead. Do you have any ideas on rebuilding the stock YFZ450 shocks?
I had the MX port with my cheetah power valved cylinders. They were the smaller set at 392cc. They took a thrashing and were as durable as any setup. They dynoed at 80 hp with about 45 ft lbs of torque. Real smooth powerband bottom to top. The nice thing with the powervalves is you can gear it really high for some awesome top end speed and still have the power done low when you need it. If you are serious about going with a power valved motor for this race you can't go wrong with this setup. I believe the RZ jugs take a little more then just mounting them on the case. The power valves are electrical on the RZ jugs and take a little extra wiring. But BenBB or Meat could fill you in on those cylinders better then I could.
Some of the best riding I have done has been at the Little Sahara with snow covered dunes. It wasn't completly covered, just on one side of the big hills. It is a blast doing 3 360s sliding down the bigger hills.