I use a canon 1dmk3, and I recently got the chance to trade my Canon 70-200 f/4L for a Tamron 70-200 f2.8 (non VC) without any money involved (lens for lens).
I'm using my lens and sometimes I miss the extra stop. I shoot portraits, small parties and motorsports. I've read that the Tamron's AF is not the fastest one, but would I be able to shoot motorsports? I know the tamron is not appropriate for that, but would the 1d make it possible? I want to trade, but If I'm not able to shoot moving subjects and get a big keeper rate (like I do with the canon), I wont do it. Any opinions?