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They are very close to each other when it comes to AF and IQ, ignoring the crop differences. At ISO 3200 and lower, the 1D3 is cleaner, at 3200, the 7D starts to match, and at 6400, they are very, very close in performance. The AF on the 7D is configurable like on the 1D3, and IMO is pretty close in performance, with the 1D3 maybe just a tad faster overall.
That all being said, the 7D isn't going to be any different at high ISO than your T3i, and quite honestly if you go with the 1D3 expecting much better ISO, you won't see it there either.
So that leaves the AF, which will be much better on the 7D or 1D3 over your T3i.
Here are some indoor basketball shots from games this week, the 7D locks focus with the 70-200 quite well, and the high ISO works well enough.