Update taking too long
Yikes, I'd be scared to look at your transaction log. This needs to be run in batches. You can experiment with that to determine the fastest runtime. What I like to do is strip out maybe a million or so records, then run updates in various batch sizes, like 1k, 2k, 5k, 10k, at a time to determine the quickest. I've done several hundred million row updates in an hour before. Then again, this also depends on the data size and I'm hoping you aren't messing around with blob fields.