Neither, instead you'd see the most overall benefit from 4X2GB Crucial; you'll also need a 64-bit OS to access >4GB. If you had an SSD then I would recommend the ReadyBoost only to take the wear off your SSD. The benefits occur only with low physical RAM.
My advice is forget the ram and get an SSD (solid state hard drive) for your boot drive. The system improvement is nothing short of astounding in actual use.
Otherwise you have a nice setup. Sometimes the little things can make improvements....one of the most overlooked programs available is Microsoft Cleanup. You'll find it in the accessories section in your menu. Run it once a week to keep the junk files cleaned up. Also, download CCleaner free off the internet.....it is a good program and helps to keep things running better.