No. The only time it would make a difference is if your computer were trying to use more than 6GB of memory... but you have the page file to compensate for that.
(You'd also have to buy a full 8gb kit - you couldn't just buy a 2GB stick, unless it were the exact same model that's in your computer.)
If you're trying to speed things up and make windows feel more responsive, buy an SSD and re-install windows with the hard drive formatted and unattached. THAT will make a huge difference.