I went from 70-200 f4 non-IS (bought $600, sold $600) to the 2.8 non-IS (bought $900, sold $1000) to the newest 2.8 II.
There was a drop in IQ from the f4 to the old 2.8 and a jump up with the new II. Focus with my 1DII and the new lens is quick and tracks very well. As the kiddos get older and play on a larger field the 200 becomes too short. I can imagine with a 5D it would be way short. If you don't need the 2.8 for night or indoor, the f4 is fast, sharp, clear, crisp...
You shoot a lot of people, non action, do you need to upgrade for that? To move into kids playing sports the better upgrade would be a 1D series to drive any of the lenses in your current kit. For action sports, spend $500 on a used 1DmII and you will be better off with your current 70-200f4 than a $1400 upgrade to a 2.8II with your 5D. The 1.3 crop will also work in your favor.

