I'd agree with Palum, if you haven't seen ANY other houses in your price range that you would be satisfied with, don't sell your house and put all your eggs in one basket. If you guys aren't super picky, or waiting for the "deal of a lifetime" type price, and would be perfectly happy in whatever your 3rd or 4th choice would be right now, then go for it.
I'd get on Zillow, look around a LOT in your price range and see if you can find at least a handful of houses on the market, right now, that would meet your criteria and at least look like you'd be happy with them. That would be a good sign that even if this house fell through, you could still find a new home you'd be happy with.
If this house is a once in a blue moon opportunity and you don't like anything else in your price range thats on the market right now, that's a HUGE risk.
I guess if nothing else, if you put your house up for sale I'd be calling the other bank/selling agent DAILY to see if any other offers have come in on that property, and yank your house off the market as soon as one does. The really dicey time period is going to be once you get your house under contract, but it still hasn't closed yet and you're waiting for that 30, 60 days or whatever. Once you hit that point there's no going back.