I have PowderHounds on my 08 TNT with a 141 X 2.25 track. The Powderhounds work pretty good under most conditions, but are downright scary with crusty snow as far as darting, have a total mind of their own and they keep changing it. My PowderHounds on the old Rev chassis worked awesome, not quite as good on XP.
Over on dtalk XP mtn section theirs a 18 page thread (Ski Test) on putting Pro Grippers on Xp's with results and how to simply do it. And you don't have to pay to read the entire thread!!
I will be getting a set of Grippers and likely selling my PowderHounds.