Getting a SSD for the application you wish to run "Faster" will give you a more noticeable performance increase than actually upgrading the amount of RAM above 6GB
Literally the ONLY time you will see a performance increase is if you use an application like Flamewave or Combustion that can assign specific amounts of RAM to specific tasks.
For gaming and general use, 4 GB is actually more than enough
Rather get a bigger lcd if you realy want to upgrade or get rid of that 4890 and get a 5000 series or a gtx 400 series