I just wanted to say how happy I am with this lens on my 5D classic. I went through hell trying to find an affordable lens that would focus well on this camera. Then I happened to pick up this well used Tamron for $260 about a year ago on Craigslist.
It's funny how much stuff Tamron prints on the lens: Tarmon SP AF Aspherical XR Di LD (IF) 28-75mm 1:2.8 MACRO 67mm
This lens focuses quite reliably even in low light and it is pretty sharp wide open. If I stop down a little it makes my old 5D classic look like a Mark III. The sharpness is stunning. It's not stabilized, but I shoot with strobes a lot so that's not an issue.
If I put a UV filter on it, I get some lens flare from the strobe behind my model, so I just leave the filter off. No flare at all then!
I know from sad experience that lens performance varies a lot from copy to copy, even with the most expensive lenses, so your mileage may and almost certainly will vary!
Mike in Vancouver, WA