my 40D was better in the AF and handling department than both my 5D and 5D2. better point spread, quicker and more reliable (though i would suspect that the quicker fps and shorter blackout time added a bit of placebo effect to this feeling). no scientific tests here, just experience from field use. ymmv.
the AF in the 5D and the 5D2 is ok, but it is not up to par for fast moving action, especially compared to a 7D or any of the 1D types. If you want full frame with better autofocus, I would suggest a 1Ds Mark II or a 1Ds Mark III...
