I shoot with the exact set-up all the time. I do a lot of kids sports and the 2x behind the EF70-200mm F/2.8 L IS USM works great for me. I've used the combination on my XTi and my 1DMKII, both with good results.


One note, this is a daylight combination. For football under the lights, f/5.6 puts me at speeds below 1/100 and motion blur starts to be a bigproblem.


I have a lot of examples. Drop me your e-mail and I'll send you some unretouched files to examine.