I tried this for the first time today, starting with Kai's recommendation of 2%. That didn't "feel" like enough to uniformly wet the grains, so I went to 3%, which may have been too much. It took a huge amount of force, and almost half an hour to mill 10 lb of grain, versus about 10 minutes last week. The crush was simply beautiful though; when I run my hands through it the individual grains are clearly separate, and there's basically no flour. Runoff was a little faster than usual, about 10 minutes vs 15 (single batch sparge). I also got a little bit of a bump on efficiency, from 83% to 87%. This is only my second batch with my Barley Crusher though, so I can't say definitively if that's a result of the conditioning.
All in all, I'll be doing it again, although probably experimenting with a little less water to see if I can mill it without herniating anything.