I have a 13-inch Early 2011 Mac Pro. I've upgraded it with a 120 GB Mercury Extreme SSD, and then I removed the SuperDrive and put a 7,200 RPM 750 GB HDD in there. I'm considering upgrading to a new 13-inch MBP w/ Retina Display. I just went to look at the specs. Seems they come with an SSD, but there's no internal SuperDrive, and thus I assume no ability to add an HDD. Is that correct? I guess I could use a Thunderbolt external HD if I need more storage? How much of a difference is there, really, between the 2.9 and 2.6 models?