My son has a gaming pc. I am considering an upgrade for his Birthday.
He has :
MB Asus PQ5 Pro Board
4 G DDR2 PC6400 (4 X 1 sticks)
Intel Core 2 Duo E8500 3.16 GHZ
Sparkle GEFORCE 9800GT 1 GB 16X PCI-E

What should I upgrade for a better gaming experience?
Double the RAM (to 8 GB)? , get a better Video Card?, or Processor?

I would like to spend around $300. What should I upgrade?

Thanks!
mac