I currently own a 20D with a 70-200 2.8L and I recently purchased a Sigma 120-300 2.8
The Sigma worked beautifully through a hockey and football game in relatively good light and temperature. However, when I brought it out to shoot the sectional semifinals out here in 34 degree Minnesota, the HSM decided to stop working.
I brought it back in from the cold and it worked perfectly. Pretty sharp, too!
My question: I'd rather not have a lens that can't take everything within reason I throw at it.
I will be shooting hockey and basketball more often than any field sports, as the soccer/football season here is over, at least for me.
Would a Mark IIn/40D + the Kenko 1.4 teleconverter produce better AF results than the 20D? Most football fields here are surprisingly well lit, so when next year comes around I won't necessarily have to rebuy the 300 2.8
I would like to keep the Sigma, and maybe buy some sort of cover for it.
Any recommendations are welcome!

