I've been following the Gingerbread thread on Motorola's Droid X support forum to see if there's any new info for a little while now. Today, Matt, the forum manager had this to say in response to someone asking whether or not he'd be able to get the OTA if he had installed the leak:
"But it does give me an opportunity to say that you are right about the actual update. If you're not on the expected software, you won't get it. So this isn't a very good idea."
Going by that, I'd say you definitely would have to SBF back.