I bought a 7D when they first came out to replace my 1D MK II. Bad move! I returned the 7D and found a almost new 1D MK III for a couple hundred dollars more. It was much better, and would autofocus with a 1.4TC on my 100-400mmL giving me a slightly longer equivalent focal length.
After a couple of years, the 7D dropped in price so much, that I bought a refurb on the Canon Loyalty program and the 1DMK III had gone up in value, so I sold it for twice the price I paid for the 7D. I mainly use the 7D for product photography tethered to my PC, and my 5D MK II for everything else. The 7D does like my 100mmL and my 100-400mmL too.
A couple of weeks ago, I needed a low light camera for two upcoming jobs and, since I did not expect my D800 to arrive soon, bought a used 1D MK IV. Obviously, its much better than the 7D. Then, my D800 suddenly arrived, and I was able to use both. I really don't want to let go of either the 1D4 or the D800, but one has to go, I can't afford lenses for both. The D800 focuses better in low light and takes TC's for f/8 AF, has a built-in flash to control external flashes, a built in AF assist light, lots of small things that make life easier, but the huge files are slow to process.
I was planning to upgrade computers when windows 8 arrived, I might do it sooner. i've been pricing build my own versus buying a Dell, it looks like a Dell costs about the same after my employee discount, and I get a warranty.