I also have read the reviews. Yesterday I got the Canon 24-70mm II and the Tamron 24-70mm VC at once to be tested against my Sigma 24-70mm HSM:
The Sigma is the worst, particularly at 70mm. The Tamron also is unuseable below F8 at 70mm, IMHO. I would estimate only two F-stops efficiency for the stabilizer of the Tamron at 70mm. May be more with shorter FL, but I haven't tested this. The TDP test results of the Tamron at 70mm is exactly what I discovered with my sample.
Unfortunately, the long focal end of the Canon is comparably short, I guess 62mm.
In summary, I am overwhelmed by the IQ of the Canon, based on the reviews I have not expected this. The difference between the Tamron and Canon is much more than the PZ test implies.
5Dsr, G5X, Sony α7R II. Lenses: ZE 21, EF 15, 11-24L, 16-35 F4L, 17 TS-E, 24 TS-E II, 24-70 F2.8L II, 24-70 F4L, 100L macro, 70-300L, 70-200 F4L IS, 70-200 F2.8L II, 100-400L II, 200 F1.8L, 500 F4L, 1.4x III. Sigma 35+50 ART, 180 F2.8 OS, 120-300 Sports, Sony 55, 85 GM, 90 macro, 135 STF, 70-300 G