Add more memory or not ?

Bit of a job to know where to put this really so any mods feel free to shift it to a more appropriate section
Basically i am going to overclock my CPU(2.4 up to 3.0) its an E4600 on a Asrock 4 core 1600 twins P35 and im running XP. Reason i posted here is because im wondering if its worth putting in another 2 Gig of Ram while the sides off (dont ask, really).
I already have 2X1GB Patriot extreme that came as matched kit. Could i reasonably expect to buy another kit and have 4X1GB running in dual mode or would they most likely not work as a matched set ? Is buying a new set of matched 2GB sticks a better option ? Would i actually see a benefit ? I am aware of the addressing issue and that it wouldn't all be seen.
Any feed back, suggestions welcome

Thanks in advance
Mactronix