Well, no, estimated power won't be remotely accurate, but that doesn't mean that a peak of 882 watts is all that crazy. A peak might be for only one second, and lots of riders are able to hit that kind of wattage. I don't know my peak power, but I do know from a few experiences with CompuTrainers and a friend's borrow PowerTap that it's higher than 882 watts - and I'm 56 kg. If you're bigger, an 882 W peak is even more plausible. From the same CompuTrainer experiences, I know that hitting 450 watts is relatively trivial even for a little guy like me. With a real thrashing, higher wattages are possible, and I once did a five-second test at 897.

This is all totally different from sustained power. As mentioned, that 897 is a five-second average. I have no idea how long I could hold 450 for, but not long! It's the same idea with something like 882. If your Garmin is telling you that you were putting out that power for a sustained period of time, that's messed up. If it's saying that you peaked at 882 on your ride, that's pretty plausible, even though chances are that it's a highly inaccurate estimate.

If you want to get a power meter, cool. I was seriously thinking about getting one for next season, but I decided that I really didn't need to go there. I would have been way more insufferable with the numbers than I even am in this post.