I have the sonnet now. Needed to pick it up for a travel job for a month out of state and the Magma just wasn't going to ship in time.
I must say, the sonnet is FAST. I have mine paired up with a rocket and a sonnet e4p esata card and it is just churning through the footage. We're shooting 5k WS 5:1 and I'm adjusting WB and throwing everything into redlogfim for resolve and rendering out prores444 1920 and it's doing it in real time if not faster at times (it's cold here in WA, so I'm feeling that may help as well). A three minute clip will render out in about 2 minutes and 40 seconds or so.
Only ONE thing I'm noticing. Occasionally I'll plug it in (turn the retina on with the thudnerbolt connection plugged in) and it wont recognize my esata card. Only way I get it to work is to remove the drives then re-install them. Maybe it's a thunderbolt thing? Not sure.
Retina specs are minimal, 2.3 i7 with 16gb of ram.