Thanks for the replies. Selling the 17-55 is definitely part of the plan. But I'd definitely like to hang on to the 7D. Partly just to have a backup body, and partly for the extra reach with my 70-300L for BIF and other wildlife. Though I'm sure a crop of the same shot on a 5D might be better, but the burst rate of the 7D is a plus too. And the 7D isn't getting a great price on ebay or craigslist it seems, so I'll probably just keep it for convenience.
But I think I will wait and buy the Canon 24-70. Since my justification for buying the 5DIII was to get a more pro setup, it seems like I should wait for the better lens as well.