Just running a quick test and this squirrel was nice enough to model.

My 100-400 II w/2xtc. So, 800 mm f/11. The MTF of the 200-800 at 800 is better than the 100-500 w1.4xtc at 700 mm, I would expect the 200-800 to be even sharper with 2/3 stop light advantage over this setup (see 800 f/11 vs 700 f/10).

Overcast day...hidden under a few leaves, but 1/640, f/11, ISO 12800 adjusted +1.1 EV, shadows +49, Whites +46 with AI Noise reduction in LR.

TDP--4 by kayaker72, on Flickr


AF was slow, but I very much suspect that is 2xtc/EF mount as every review I have seen talked about how AF was as fast as f/2.8 lenses.