I've never tried P90, but I've read enough about it to know it doesn't interest me. It sounds like it's quite a bit less intense than P90X.
Power Half Hour or P90 Masters would be a step above Power 90.
If you can already do all of Cathe's workouts with no problem, then don't let P90X discourage you. Chest/Back can be a pretty intimidating workout (the reason I let P90X sit on my shelf for several months before even trying it---all those push-ups and pull-ups were too scary!!!). But as Anne says, you can do substitutions for the pull-ups/chin-ups. I stated by doing heavy 1-arm rows (alternating sides with each set) and pullovers instead of the pulls and chins. Then I progressed to the Beach Body bands (the heaviest set) with a door attachment (the Sissel attachment, which is much better than any other attachment I've seen).
I also started P90X with "Shoulders and Arms" (which quickly became my favorite P90X workout) to get around the dread of doing chest/back (I continued the rotation from there, and did do chest/back, just out of order).