I just got a WD MyPassport Studio 1TB drive for backup purposes (1:1 clone of my OSX Lion drive in my MBP) and it came pre-formated in APM. I noticed this only AFTER spending 7 hours of backing up all of my data to it. I can boot cloned OSX Lion from it normally, but it's not very fast (FW800). I am just wondering if it would be any faster if I re-formatted it to GUID table? File system is HFS+ (Journaled). PS: I use part of that WD MyPassport Studio for external storage. Would I benefit anything by going from APM to GUID? Again, the partition is HFS+ (Journaled).