Personally, I would buy the 820 and then sell or trade in the 6600. Sounds like you "settled" for the 6600 at the time (even though it is a nice machine), but now that you can afford the 820, I say go for it. It will probably be the last sewing machine you buy, so why not have everything on it that you want. Just my humble opinion, but that is what I would do. This is money that you hadn't expected and didn't have it earmarked for anything, so I would make the purchase of the 820.