So I just received my 5D3, love everything about it, but had one idea that I can't seem to make work how I wanted, so I present it here:
The plan is to use an Eye-Fi card in the SD and send jpegs over to my iPhone linked in direct mode while I'm out shooting for instant upload to facebook, twitter, insta.. whatever. I don't want every shot to be a jpeg, just want to be able to choose a photo here and there to send to the iPhone. I figured out the one shot RAW+jpeg thing and tied that function to the M.Func button and that works beautifully, I can shoot all RAW and then decide the my next shot should be a jpeg, press the M.Func button, shoot and I have a RAW+ jpeg recorded, then the camera goes right back to shooting RAW only. The next step is to have RAWs recorded to the CF card and jpegs recorded to the Eye-Fi SD. This I figured out pretty easily as well but when setting the record separately function on the cards I lost the ability to do the one shot RAW+jpeg thing, the camera shoots a jpeg and a RAW on every shot (not what I wanted).
Next I thought I could outsmart this problem by using the custom setting modes on the main dial (C1,C2,C3) and tie one of the modes to only shoot jpegs and use card 2 (Eye-Fi SD) instead of my default card 1 (CF). This way if I was in the field and decided my next shot should be a jpeg for instant sharing on my iPhone, I just spin the main dial to C1, shoot, then turn the dial back to whatever mode I was shooting in. The quality setting of jpeg is setable to a custom preset mode (C1) but the card onto which to record seems not to be... Canon if you're listening maybe a firmware update? Anyway, if anyone here has suggestions on how to accomplish this one off jpeg to an SD card idea I would love to hear your thoughts. Thanks!