Ack help with ram purchase.

All of a sudden I need to upgrade my computer tonight.. Long story. Anyways I was going to place my order at newegg when I noticed that there is ram faster than pc3200, I didn't realize that. I plan on getting a 2.2 ghz amd newcastle 64 processor and I am wondering should I get the pc 3500 3700 or even 4000? I dont want to spend the extra money, but will if it is a big deal. Any input would be greatly appreciated. I am under the gun though as I have to disassemble this computer shortly and will lose internet access. Thanks everyone.

the best way to find out is to ask the guys already running that kind of setup.(mb and cpu) that way u know what speed ram to get..