I had an excellent copy of the 28-70 that I sold on here last year. It was great BUT was heavy and I never really used it. I also was afraid that if something went wrong with it that it would be an anchor.
I decided to give up the mid range zoom and pick up a few primes instead. You might consider this. I now have the 35 f2 IS and the 85 1.8 and love them both way more than the zoom. I really don't miss the zoom.
If you absolutely have to have the zoom then don't discount the 24-105. Or save a bit more for the 24-70 mk1... Or even the newer 24-70 f4 IS.
Anyways, something to consider.