Canon 70-200 f2.8 mk II or Sigma 120-300 f2.8 OS

[Canuk]

Wondering on opinions on these 2 lenses. I currently have the Tamron f2.8 70-200, and I am looking to replace it.
I generally shoot a lot of motorcross and outdoor photography. I currently have the Canon 60D, but am looking to replace it w/ full frame depending on what the 5D mkIII brings.

I know the Canon 70-200 mkII is an awesome lense w/ very few problems, but when I do switch to full frame I will be loosing the equivalent focal length of 105-320 (if my maths correct). So would the Sigma 120-300 maybe be a better bet?
The cost of the lenses is pretty close ATM w/ local retailer selling the Canon for $2529 and the Sigma for $2999.
Just curious on other's thoughts.

 

[Overread]

You can see some of my early views on this here: http://www.thephotoforum.com/forum/...72194-sigma-120-300mm-f2-8-os-has-landed.html

Personally I think either one would suit your situation - however bare in mind that the 120-300mm is a much heavier lens. Certainly you can use it bare without a 1.4TC and get a good long reach, but it will be heavier and bigger than a 70-200mm with a 1.4TC.

 

[Canuk]

Thanks for the response. I have been following your thread on your Sigma 120-300 OS lens. I was interested in hearing from you because you have first hand experience w/ them. I will try to maybe borrow a friends older 120-300 and see if the weight is overly objectionable, I am so used to shooting w/ my Tamron and 24-70L that I think a light lens maybe more uncomfortable,