Although I have a Pegasus R4 I decided to buy a dedicated off Mac solution for my (512GB) rMbp, so went with a WD 2TB drive, formatted it for Mac, and will now consider just how I'm going to use it. The rMBP is a work tool where as the MBA it replaces was not.
I plan on keeping my photo work and current project fies on the WD which although only USB 3 I'm finding surprisingly fast...it's never going to be quick enough to work on files in real time, but with half of the original SSD space still left on the new Mac, and 2 TB with the WD, I think I'll be fine for space....I can move data around and all backups are on my 3TB TC, with mission critical data further backed up to the Pegasus unit.
I plan on keeping my photo work and current project fies on the WD which although only USB 3 I'm finding surprisingly fast...it's never going to be quick enough to work on files in real time, but with half of the original SSD space still left on the new Mac, and 2 TB with the WD, I think I'll be fine for space....I can move data around and all backups are on my 3TB TC, with mission critical data further backed up to the Pegasus unit.