Usually your ram runs in synch with the fsb, so if you buy pc3200, you'll be running it at pc2700 speeds. (actually PC2912 because of your OC). However that means that maybe you can tighten the timings a bit and reduce latency, which would improve performance a little more. And, depending on what you're doing, the extra RAM may help.
Also, having pc3200 ram may allow you to upgrade cpu/mobo without having to buy new ram in the future, so if you do buy new RAM, get PC3200.