Excellent review. I've had this lens for nearly 2 years and use it primarily for shooting football (soccer) matches and it is just superb. Matched with the 1Dx I rarely miss a shot and if I do its usually my fault for setting the camera/autofocus wrong. I agree the only real downside is the weight, it really is heavy at circa 1.4kg. The use of a Black Rapid strap has helped big time though.
If you can afford it this lens is without doubt the medium tele-zoom to buy. That said I've considered re-purchasing the F4 non IS, just for its low weight, it is a great lens too.