If you're talking about firewood for your personal use (i.e. not a business) then I seriously doubt your 455 is holding you back at all. Cutting the wood is a small percentage of the time spent getting wood to your stove. My dad's 455 will pull a 20" bar fine in anything I need to cut, and even if you sometimes have to cut from both sides it will hardly slow you down. You could even get a 24" bar for occasional use.
If you just want another saw that's cool, but don't expect it to result in bigger stacks of wood. You should decide how big a bar you want to run and pick the saw based on that. My biggest bar is 25" (84DL) and I've dropped 30" trees and bucked 36" with that, but we really don't have many trees of that size left here.