When I say noticeable upgrade I'm looking for appreciably sharper. I've got the Tam 28-75 2.8 (plus a lot of letters I don't know the meaning of). I like it a lot, but I'd like to get something just a little bit sharper. So obviously I should just save up for a Canon 24-70L version 2. But that's out of my price range.
So I went to The Digital picture http://www.the-digital-picture.com …omp=0&FLIComp=4&APIComp=0![]()
and looked at everything in this range, mostly checking on the long end. None of the Sigma's appear to be sharper. The Tamron 24-70VC does appear to be quite a bit better but I'm wondering if there is something else in between I'm not aware of?
TL;DR Is there a 24-70 2.8 lens that's less than $900 used, but appreciably better than the Tam 28-75?

