First image is the bare 600/4 II. Second image is the 600/4 II with the 1.4xIII. They were actually shot 1 week apart, and with full disclosure, the bare lens takes a hit for being shot on a cloudy late afternoon, while the sun was shining a week later when I returned to the same spot. So, the bare lens image is f/4 ISO 6400, while the 1.4xIII is f/5.6 ISO 3200.
The last image is a pair of 100% crops, bare lens on the left, 1.4xIII on the right.
You be the judge...
What I find most interesting is that you apparently have a trained, pet squirrel!
Seriously, though, I think the cloudy day made for a better background, even with the additional noise.
yeah hurry up with the 5D3 firmware already and include the option to program the rate button to other functions too please!
+1 I'd like to be able to toggle the VF grid on/off with it.