I want to get a new internal hard drive for my Mac Pro to run Time Machine. Basically my plan is to get get a 3TB drive to back up my .5TB, 1TB, and 1.5TB drives currently in the machine. Currently I have the 1.5TB drive backing up my .5TB and 1TB drives, and feel it's time to expand my storage. My question is does the drive speed of this new 3TB Time Machine drive matter when considering 5400 RPMs vs. 7200 RPMs? I would think it doesn't matter much, but with the constant writing that Time Machine does, would I see any performance increase by going to 7200 RPMs? All my current drives are 7200 RPMs if that matters. I'd just really like to save some money if possible, but not if it means I'm getting lag every time a backup starts or something.