Here we go with more pixel peeping. 100% crops from my new 70-200mm f/4 IS.
Shot at 400mm effective, f/4, f/5.6 and f/8 (f/8,f/11,f/16 effective). Looks pretty sharp to me, and my 1Ds Mark II did auto-focus!
Surprising quality, given that this was a cheap TC for $90,bought from Adorama after a positive review from Shutterbug.
For comparison, the second photo is at 200mm, same apertures, without the 2x TC.
More to come this weekend!