I've been mulling this over for a while, but I'm considering the 200 f2. Attach a 1.4x and I'm at 280 f2.8... not quite 300 f2.8, but not bad either.
With a 70-200 f/2.8 IS II in tow already, why the fascination with the 200 f/2? The 300 f/2.8 IS II is so much better than either 70-200 or 200 f/2 IS at 280. Just curious...
I can probably afford the mk i version of the 300 f/2.8... so that's the one I'll compare.
And with the 1.4x, the 300 still wins... but it isn't a blowout victory. The 300mm f/2.8 mkii is closer to a blowout...
But, what the 300mm can't do is shoot at f/2... and that extra stop of light means and 1 less stop of iso.
I'll still use the 70-200, but I do shoot some sports where there is quick movement, but at specific locations... volley ball for instance. The serve is always from the same location... the net is always at the same location, though the players obviously move up and down the net.
Ditto with tennis. I just like having the flexibility of f/2, f/2.8, and f/4... I know the stand alone primes are better individually, and I can use the converters on them... but I generally don't shoot at f/5.6 unless I have to... so give me 400 f/4 v. 600 f/5.6...
though I may be capricious about the whole thing... so I might change my mind tomorrow.