I was finally able to try mine out on monday on my 08 d7. I really like it so far, my sled feels alot snappier, it is really smooth going from reverse to forward now. I am running a 73/59 helix with a red/dark blue spring which is 20lbs softer on the bottom and 40lbs softer on the finish rate than what I was running before and it still seems to backshift really well. My rpms stayed pretty consistent.
I checked the belt after playing around in some descent powder and I could touch it with my bare hands, something I couldn't usally do with the tss 04 so it must be working more efficiently.
I was riding with my wife so I didn't get a chance to compare it to any of my buddies sleds, one of which is a stock d7, to see how much improvement there really is. Seat of the pants feels pretty good but most sleds feel that way when your by yourself on the hill.
I will report back again when I get a better comparison