I get that you only have so much to spend, but I'm tellin you don't waste your money on a plastic cased saw if you want it to last. I've got no doubt that the 455 will last for some time, but the commercial/pro grade saw will outlast it twice and you won't have to go through the hastle of figuring out what to buy a few years from now when the 455 kicks the bucket. Any good dealer will let you test out the saw, IMHO it would be real poor service to sell something to somebody having no understanding of what it is they are buying and not giving them the hands on comparison between the grades of saw. My local dealer does and they aren't a huge place, and then sell the demo's every so often.
If your dealer is letting people demo saws ask if they have any demo pro grade saws for sale. I've seen people get sweet deals on demo saws and they have been in great shape, but its up to your dealer to back the saw if you're buying that way. If you ask you may be surprised, that 550xp may be closer to your price range than you think.