I see that the Black version is 7200RPM , but the actual read/write speed is the same as the Blue? The Blue version is 5400 rpm only, and goes to a maximum of 500gb while the black goes to a maximum size of 320gb? The black also has 16Mb of cache while the blue only has 8mb of cache. So why would i want to buy the black version, is their really a performance increase?