I also dont know much about the 454, but i searched around for a few minutes, and it appears that 360gr is the highest 'factory/standard' bullet weight. in fact, i checked a few powder manufacturer sites (Hogdon, etc) and none even listed data for 360gr. 300 was the highest shown, so looks like 360 is about it.
I work with a guy who has a 454 and he loves it. says recoil takes some getting used to, but isnt bad at all. he tells me he is planning on trying out the corbon 360gr rounds this weekend. if i hear from him, i'll ask him about it and see what he says.