Hi, I'm looking at getting a new 15" MBP and need the storage of a HDD and would like the speed of a SSD, logically leading to the optibay solution. I would order the MBP with the 128gb SSD already fitted leaving me to upgrade the superdrive to the optibay + HDD. However which is the best (750gb?) HDD to use. I have been reading that it is essential to get a drive with a motion sensor built in as if the drive is in an optibay this is not provided. Which HDDs provide this technology? And any other recommendations? Thanks.