One thing I did notice, that mother board you linked supports dual channel memory but the picture your posted looks as if it only has 3 out of the 4 slots populated.... This means that your memory is operating in single channel mode.
I would say remove/add one stick but that depends on how much RAM is there and also what speed it is and if you do decide to add a stick get ready for some sticker shock
DDR2 is now way more expensive per GB than DDR3.
Just something to keep in mind.
I run an OCed E8500 myself with 8GB's of dual channel DDR2 800 that pairs up nicely with my 1600Mhz FSB
lol