Just did this with a t2i and I was happy until I heard about f8 AF on the 1dX. Now I'm not so sure I made the right choice. You'll probably get more pics out of the 1d MkIV but your going to be taking more pics so... They definitely will look better than the 7d as long as you're not in really bright light with a stationary subject.
Well, $2k plus a 7D, which means a total cost of a little over $3k...vs. $6800 for a 1D X? If someone can afford the 1D X, they generally wouldn't be fussing over a 1D IV trade for a 7D like that. My guess is the 1D IV will be a superb camera, and a great step up from the 7D, despite the new 1D X firmware and its added f/8 AF.