The 800 tripple makes more Horsepower overall, somewhere around 150 if it has tripple pipes, 140 without. The ZR 800 has about 140 HP. It will be a close one, and it may come down to if this Polaris sled is an XCR or Storm. Either way, Arctic Cat has the power-to-weight advantage here, so it's definitely going to be a close race with out without pipes.
The lighter Cat would be faster on a short run, and the triple would have longer legs!
That being said I have a pair of 800's myself, ZRT800 and ZR800. And my ZRT doesn't even hook up the track till about 70! And is capable of over 125mph! The twin has ALOT of low end grunt, been known to chew up trees and spit them out! But both will turn in 97-99mph in 500 feet!