I'm planning on building a gaming pc in the next few weeks. Currently I selected the Western Digital Caviar SE16 WD7500AAKS 750GB. I have read a couple of articles saying that the cheaper Western Digital Caviar SE16 WD6400AAKS 640GB is a faster performing drive. I haven't found any concrete facts besides the platters being denser for the 640. I don't know by how much faster is the 640 over the 750. Which hard drive should I choose? If the 640 isn't that much faster than the 750 then I could definitely use the extra space. The 750 also has a bunch of features I don't see in the 640.