I'm about to buy the new (or newly updated anyway) Retina MacBook Pro 13", and the one thing stopping me from pulling the trigger right now is storage. I'm looking at the 128 and 256 gig from B & H Photo, a MacRumors partner. They are $1229 and $1400 respectively. Of course I'd like the most powerful MacBook I could get with the best processor, abundant RAM, and plentiful storage, but I just don't have that kind of money at the moment. I wouldn't mind spending that couple hundred more for double the storage, but I can always easily double the storage later on with flash cards and sticks, and even more so with hard drives. However, anything read from or written to these expansions would have slower speeds than Apple's built-in PCIe-based flash storage, correct? I know a hard drive definitely would. I'm just worried that, even with all the RAM in the world, an application I have cached on an external source would open slower simply because it had to travel through a slower bus.