We have all seen the pros with their 800mm lenses at the sidelines of football games. It is great but most of us can't afford that.
Have you considered using a monopod? At your son's soccer games you may find that the referee thinks that you are from the local paper so you may be able to get closer. A big lens with the hood on (even if you don't need it) helps too.
my 2c worth - I like the 70-200 f/2.8 VR, It is very sharp and I am still happy with it on my D800. Late in the day the faster lens is an advantage but if your budget is more for the 70-300 VR go for it. Capture the images now. Don't wait until your son has graduated because you think that you will be able to afford the lens more expensive later.