Upload & Sell: On
Sports photographers preferred f/2.8 because until recently, the high ISO performance of digital cameras, and before those, film, made it pretty much mandatory. With recent cameras it's not a biggie to shoot ISO 3200-6400 to facilitate f/4 or f/5.6. Sure, there's the subject isolation factor as well, but IMO it's, to a degree, a secondary consideration to other factors such as convenience and versatility.
Ron, then, why not get 100-400 ?
It is much much lighter, much much cheaper than 200-400L, and also it has a broader FL range. Moreover, you can slap 1.4XTC on it and it will AF with your MkIV.