« on: May 29, 2014, 12:09:41 PM »
I'll reiterate what StudentOfLight said about the Tamron. It's a shame that you aren't considering it. I have a 6D and the Tamron 24-70 VC and haven't missed the Canon Equivalent at all. As much as it pains me to relive this, the lens has fallen out of my bag once and was on my camera when my tripod tipped (cheap tripod) and still it performs flawlessly. IQ is sharp and the VC definitely helps in the lower light.
My copy, although great, was my second copy. You just have to test the sharpness when you get it and if it's not up to snuff, return it. Also, the Bokeh isn't the greatest. My copy does have that onion look, but for the most part, it's a non-issue.
I've compared my Tamron to a 24-105, and the mk1 24-70 and blew both out of the water. I haven't been privileged to play with either the 24-70 f/4 or the mkii 24-70 2.8, so I can't say where it is compared to those two. I will say that based on how recent the mkii just came out compared to how long the 24-70 lasted and the old 28-70, I think you'll be waiting at least 2 years before you'll see a 24-70 2.8 IS, but that is just my guess.
I would say your biggest question would be whether to save the money now with the f/4 IS or go big with the f/2.8. Which ever you do, don't look back and you'll love your decision