I have owned and used both of these lenses extensively for wildlife shooting. While the OS version was great, the Sports model quality really blows it out of the water when used with teleconverters. The OS model handled the 1.4 very well but with the 2.0 you really need to fill the frame for great results. With the Sports model, the 2.0 only comes off the camera in very low light situations.
All of my friends and family noticed the difference in my images immediately when I started shooting the Sport model.
The 2.0 on the OS version was not fast enough for BIF, but I even shoot the those subjects now with the Sport model and the 2.0 combination.
No comparion in my mind, the Sport model is a far superior lens.