which focus point/s are you using? you'll probably find an increased accuracy when shooting centre only
not my 5D2's i just use them ive used them with 70-200 2.8 IS (IS off, hate the bloody thing) and the 24-70 2.8
the images that come out are awesome, i happily shoot speeches ISO3200-5000 without flash
i prefer the crop sensor to FF, my shooting style is such that i like the extra reach i get using the same glass.. if i had a choice id shoot the speeches with 40's instead of the 5's because i can stand at the back of the room instead of the middle.. i think i could live with the 1.3 crop on the MKIII for sniping and a 1Ds for portraits..