Hi there,
To be honest the difference isn't really that great and, as you have a BE CPU I'm surprised you don't run your RAM at 800 Mhz and up the speed of the CPU which will, in real terms, give you a much bigger system boost.
Also, if you are running a 64 bit system, you could actually re-install the 2 older sticks (fill all RAM slots) and run with 6 Gig of RAM which would also help, although you would have to stick at 800 Mhz.