I want to install an ssd in my lower optical bay and install the OS and applications? My question is what size SSD would be sufficient. On OWC's website the price difference between the 240gb and the 480gb is $900. Will the 240gb be sufficient for the long haul or do I need to bite the bullet and get the 480gb? I will be installing 4 2gb Hitachi drives in the other hard drive bays. Thanks for your help.