I know exactly what you mean about the banks dragging their feet, but some will, some won't, and may react differently even with their own properties. Moving quickly isn't a sure thing, but if a bank, owner, or builder wants to get a home off their books, hesitating can often automatically take you out of the running.
Really, it's not much different than what you can run into anywhere in the market, not just REOs. Builders can stand firm, then for whatever their reason decide to offer greater incentives or go lower price. Resale owners rejecting offers can have a sudden change of heart and trim their asking for a quick sale. Once there's a great deal it's bound to attract attention. Some will wait to see what comes in, others are ready to go. It's why you have to stay on top of what's happening, and why I tell my buyers not to limit themselves, especially to "only foreclosures". That label doesn't necessarily mean more choices or a better value. I think it's good idea for you to consider the builders, just in case.
That home I mentioned in my last post is a perfect example. The buyer had an offer in on a short sale and no response from the lender for weeks. Then a builder's model home came on the market one night. Professionally decorated, upgraded, furnished, and on a landscaped over-sized lot in the area they wanted to be. Best of all it was 40k under their previous bid and didn't need the additional investment of the other property. No, it won't happen every time, but a good reason not to restrict the possibilities.
Sure it's a bit of luck, but mixed in with some perseverance, a little creative thinking, and staying tuned in to everything out there. I was making my own move to Vegas when the market was crazy. 6 months of searching and so many offers above asking accepted before mine could be presented, missing some by just an hour. Builders were struggling to keep pace with demand and new homes meant waiting months. Some places had you wait for lotteries just for building lots. Having sold everything on the other side of the country, the pressure was on and yes it was frustrating. Then I found a home that also turned out to be an REO. It was larger than I what I had been bidding on and yet below the increased price range I began using to increase my own chances. A really tough find, especially in a sellers market.
In this business just like any other, if you give up, guaranteed nothing happens. Work harder for a solution to overcome the hurdles and you're still in the game. Lowering the size of the home opens up more selections in your price range, and still doesn't eliminate what your looking for should it turn up.