My Tokina 300mm F/2.8 with Kenko 2x converter worked, 600mm F/5.6 with AF working etc, although, AF was inconsistent, rather inaccurate at times, and the image quality suffered. aberrations started appearing with the converter etc...
The 70-200 L lens with the Canon 1.4x converter (that I bought off Doug, whom instantly regretted it, and bought another
) produces outstanding results.. image quality seems spot on, sharpness, AF reliability is still top notch...
Its a winning combination thats for sure.
Alex.