Bottleneck is a general term used to mean that is what would be slowing the system down. ie, if your Hard drive is slowing your system down a lot due to it being real slow and fragmented, then you can have the world best CPU and ram, and it wouldnt help the hard drive any at all to be any faster.
I agree with Nubbleet, it will be very hard to bottleneck 4gb of ddr3.
That being said however, I enjoy overclocking everything I can frankly. I'm not bleeding edge like many, but its just fun. granted you can lose parts...but its still fun.