I am still getting some superb results from my 7D but the focussing with the 300mm f/2.8 II + 2xTCIII can hunt when there is not a contrasty subject. I got sufficiently frustrated yesterday, despite getting some good BIF shots, that in the evening I ordered a 70D and it arrived this morning from WEX. The initial results are looking good, and I'll post a comparison when there is good weather here in a couple of days. DxO tests on its sensor suggest the 70D has significantly better IQ than the 7D.
5D IV, 5DS R, 7D II, EOS-M, Powershot G3 X, 400mm DO II, 300/2.8 II, 1.4xTC III, 2xTC III, EF 1.8 STM, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, Sigma 150-600mm C, EOS-M5 15-45, f/2 22, 11-22, Samyang 8mm f/2.8 fisheye