I've demoed the Q701 in my own home for several weeks, and I currently own the 400i. At least to me, the 400i is the better headphone overall, no doubt about it.
And yeah, besides the soundstage, I can't think of anything the Q701 does better than the 400i. For example, the 400i simply has lots more bass that is still well-controlled. Basically, the 400i just sounds more real than the Q701, and this is a very noticeable difference.
At $299, this is a steal. At that price, the 400i easily competes with anything at least 2x the price.