New Build Memory Advice

Hey everyone,

I'm upgrading my rig a bit by getting a new case, MoBo, CPU, and HSF, but I had a question about which memory I should use.

I want to OC my q6600 from its stock 266 FSB (266x4 =1066) to 333, which will give me ~3.0GHz. Currently, I have DDR2-800 ram, so it's 'bus' speed is 400. I don't want to take the CPU to 3.6 (400 FSB) because I'm not an experienced OCer and I hear that q6600 aren't stable at 3.6 with only air cooling. (I am installing a Zalman CNPS9500 and plan on using a good thermal compound) So my question is, should I 'underclock' my ram to 667 (I don't have a good idea of how to do this, or if it's possible) or should I change the FSB:RAM Ratio. I hear that a 1:1 ratio is the most stable and best performing, and I couldn't find any settings that fit into the typical 5:4, 3:2 ratio exactly. Of course, my other option would be to just buy 667 DDR2, it's quite cheap. Any advice on where I can go with this is greatly appreciated. Thanks.

Also, I currently only have 2GB of the DDR2-800 and I'm running XP 32-bit sp3. Is it worth it to get another 1 or 2 GB of which ever speed I end up deciding on? Or is that extra 1-1.5 GB even noticeable?