I don't know if the focus was perfect on this since it wasn't done with 10x liveview and the AF is very dodgy since they locked out the new f/8 AF for this combo but one of the better looking frames produced this, not exactly THE sharpest thing in the world, but plenty useful and usable and with more noticeably more detail than an upscale:
I mean damn why do they have to lock out the f/8 for the 70-300L?!! It's such an awesome lens for hiking/walk-around/long landscape and to be able to use it at 300mm and pop on a 1.4x TC is one of a few of the main reasons people cared about f/8 AF ability! That would be so awesome. The results are plenty usable optically, if only it would AF! This is what we were waiting for.
Sure don't say that it is officially supported, fine, but don't lock it out either. That doesn't prevent anything. People can still pop on that combo and having it hit at the short end whether the firmware works with it or not. Stinks they locked it out.
Someone on another board claims it works with the 1DX but that they removed it from the official compat list. So why did they have to go and fully remove it from the 5D3 and not just done the same thing (assuming the story is true)?