175x1 (ie. my current body weight). Probably could have gone a bit deeper, but that looks parallel to me (at 0:20 of the video). In fact, I think it's pretty much the exact height of the box that I've been squatting with.
It's a little strange squatting with someone directly behind you, although I was glad to have Brian there as a security blanket. 175 really wasn't that hard to get up in retrospect, but there was the whole 'my hamstrings feel sore today' and 'I just box squatted 130 5x5' and 'wow, that looks like a lot of weight' thing in my head.