so, i know it's generally adviseable to buy ones own drives and RAM rather than from Apple. but, as i finalize my decision to buy a single quad core, i'm struck by the option to spend $42 more to upgrade the 320 -> 500 gb drive. obviously, it's only 180 gb, but since i have enough old drives lying around (of various size), i almost view the $42 price the price of a 500 gb drive should i buy one straight off the shelf brand new and perhaps a better option of "consolidation" vs getting the 320 standard one. so the question is this: is the 500 gb drive Apple installs worth $42? anyone know what these drives are? 16 mb cache? fairly decent speed? i'll be using this drive initially and then swapping it as a "time machine/backup" drive to a secondary bay down the road when i have more cash and can figure an optimal solution. thoughts would be appreciated and if someone knows in recent experience what 320 and 500 gb drives Apple uses/provides, that would be most helpful.