Correct answer: if when you overclock your CPU it also overclocks your memory by the same amount, then PC2700 can give you a better chance of a higher overclock and lessen the need to use slower timings. If the memory is locked at the max of 266MHz (which is very unlikely) then it wouldn't go up when you increased the CPU bus. Most probable is that your memory runs at the same speed as the frontside bus, or the BIOS setup allows you to set the memory speed separately (it's best if they're kept at the same speed). If you're using a 266MHz bus, then PC2100 memory is matched, but if you get up to a 333MHz bus then PC2700 is best, even though PC2100 will work.
You'll need to check your manual to see how the memory speed is set. I don't feel like downloading it and doing it for you.