I tried out this combination today for an experiment to see how it performed. Popped them on the old 7D and took a few shots of comorants fishing in a local river. Just got them back and whilst ive never used x2 converters before im amazed at how good the shots are (quality wise not put em in Nat Geo wise). They needed a little sharpen but printing at A3 will be no problem. The 70-200 continues to amaze me at how good it is. Hand held 200mm plus converter and 7D maxed out to 640mm and it nailed them. The autofocus was a little slow but ok for static sitting birds but the sharpness was excellent. Yes a little soft but nothing too bad at all. Canons latest glass zooms, converters and primes are excellent. Now whens me new 500 f4 gonna arrive!!!!!