Well I have ordered the Belkin adapter just to try, doubt it's going to work from what I've read. Other guy was using a 7000 series gpu, hoping it might be different with an R290. Only other adapter i've seen that I thought might be promising was the Moshi Mini DisplayPort to HDMI Adapter on the Apple site. Not sure if it's worth trying. Already spent like around 25 and adding another 35 is a bit much for adapters that probably wont work.
Couldn't even get 4k out of it. It seems the best I can get is HDMI to HDMI to get the 4k but only at 30Hz. Pretty crap but I guess it's ok for some games. Shadow of Mordor is pretty good and considering a lot of the games on the next gen consoles are only 30fps it's still a big step up I guess.