Not sure if it's better to buy an internal one and a case or just get an external one. Looking for ~500GB. How's this one? Seagate - FreeAgent Pro 500GB External Hard Drive Here's an internal one for about the same price but then I'd have to find an enclosure. Seagate - 500GB Internal Hard Drive What would be the perfomance difference between the two? The internal one says 16MB cache. External one doesn't list cache size??