Ryan, I'll take a few photos outside tomorrow with the AFS 70-300mm and the Kenko pro 1.4x. I took a couple photos indoors today but in the low light it chatters with the extender and then settles down at 300mm. And that was with the D800's improved AF sensitivity. Performance was fine at 200mm. I was 14' from the target.
But here is what I shot inside tonight. Shot with the D800 and AFS 70-300mm VR at 300mm, first without and then with the Kenko Pro 300 1.4X extender. Other than size there is no post processing. The focus point was just under the nose.
300mm full frame. Shot at f5.6 and ISO 800 with SB-400 flash.
420mm full frame. Shot at f8 (actual f11)
crop from 100% enlargement of 300mm photo.
crop from a 67% enlargement in order to keep the size comparable.