The "R" in R850, as you might guess, is for the "race fuel." We wonder if the "P" in P800 means "pump" or "plebeian." The 850 HP and 820 lb-ft numbers are the assumed amount at the crank given the dyno numbers, which show about 740 AWHP and 715 lb-ft. If you've got a GT-R and are itching to throw all warranty concerns to the wind, the package runs about $20,900 and includes the tunes for both pump and race gas, as well as a larger dual-core radiator, thermostat, and Switzer MONSTER intercoolers.
And if you can't handle the power, there's always this thing to save you.