I know I'm going to take a lot of flak for my .02, but I'll tell you what I know from first hand experience on my 04 king cat.
Hands down, I'd run the Challenger extreme, but I would go with the 162x15x2.25.
I have ran all 3 tracks. Originally ran the x15x2.25. Loved the way the sled got up on the snow, espeically in the bottomless stuff.
Then one fall I was looking for a project for my sled and decided to go to the x16x2.5. Went to the sled show and got talked into a powerclaw.
I put it on and as soon as we got enough snow, I took for a spin and was dissapointed. Hauled it back to town and spent the next day putting on the x16x2.5. Took it back up the following day to the same spot and was glad to have a challenger under me again. Almost identical snow conditions and I took lines right beside the ones I took on the pc. Hands down, on my sled, the challenger extreme was the better track in the deep stuff. The x16 got even better after a summer in the trailer (CE's are a little stiff when they are new, but after the soften up a little with time the perform better).
The reason that I say that I would just run the x15x2.25 is that I did not notice a big enough difference between the x16 and the x15. And the x16 is a tight fit. Tighter for me than many on here because I am running Holtz drop backets instead of junky's.
Most people on here that have changed over will tell you that the PC is a better track. I can only say that it wasn't for my sled.
Cheers,
Chris