As previously said, we don't know that for sure. However, in a few days I hope to answer that question in a scientific way, side-by-side comparisons.
I'm trying now to determine test methodology. This is what I've come up with so far and comments are welcome:
Test each lens as follows:
1) Sharpness Test on same subject - three images; 70mm, ~135mm, 200mm. Camera mounted on tripod at f/11 to illuminate any shake blur and depth of field blur that may be mistaken for 'softness.'
2) Hand-held test at 1/30 sec. at 200mm. This tests the advantage of Tamron's VC compared to Canon's lower f/4 (at 200mm, the Tam is likely to be f/5.6 min.)
Subjective tests: Speed at AF; feel; etc.
^^^^You beat me!!!
Why would you shoot at F11??
Shoot them both at F8...diffraction will affect the images at F11.