Have just ordered iMac 27" i7 4.2Ghz with AMD Radeon Pro 580 GPU for video editing using Avid. I would like to use a second display for my timeline and bins, and the Retina 5K for full screen playback. I like the idea of an Ultrawide like the LG34UM95 (3440 x 1440) which has thunderbolt. Has anyone tried this combo? USB3-C to Thunderbolt 2 converter would obviously be needed, but would it work? Would the GPU allow the two different resolutions simultaneously, or would the Retina display have to down-rez to HD? Thanks for any advice.