Is there any decrease/increase in performance to using 2 sticks of 256mb or 1 stick of 512mb RAM? Does it affect OCing?

I am currently using 2 sticks of generic PC2100 but soon to get 512mb of Samsung PC2700, i am not sure whether to go with 2 sticks of 256mb or 1 of 512mb. I will be OCing my Tbred to 166FSB.