Here is a shot taken with the 300mm f/2.8L IS II + 2x III on a 1Dx. It shows some inflight action. I would say this combo is very usable.
If you already have the 70-200mm f/2.8L II, I would recommend getting a 2x III and try it out at 400mm. You will be surprised by it's performance. Faster than a 100-400mm and the IQ is better.
Wow...that is an amazing photo with x2 TC III Jason. Thanks for sharing. Will take your advise and try out x2 TC III on my 70-200. I heard nothing but "WOW & AMAZING & RAZOR SHARP & LIGHTING AF" about 300mm version II.
This could be my next lens
Thanks Dylan. It is a really great lens and so is your 70-200mm f/2.8L IS II. Happy shooting!
Cams: Canon 5D3, EOS M
Zooms: 16-35mm f/4L IS, 24-70mm f/2.8L II, 70-200mm f/2.8L IS II; Primes: 22mm f/2, 40mm f/2.8, 50mm f/1.2L, 100mm f/2.8L IS, 135mm f/2L, 300mm f/2.8L IS II, 600mm f/4L IS II
Support: Gitzo GT4542LS/G2258, RRS BH-55, Wimberley WH-200