I havent seen War or Stars, Skis and Hucks, but besides those 2, I don't think he has ever topped his ski movie 3 performance. That being said, its also not his fault. He had shitty weather and snow conditions as well as being injured, in both focused and yearbook, and still had a decent segment in focused.
You also have to take into consideration that he is what, 31 now? Taking all those huge impacts year after year isn't easy on the body thats for sure. Seth is a freakin' god, and I believe, given the conditions he will continue to amaze.