Hello, I've had the i7 m395x iMac for a few days now and so far I've only tested two games, World of warcraft and Heroes of Newerth.
In world of warcraft I managed to obtain a constant 60fps in Stormshield with 5k resolution and half of the settings on ultra (had to turn down some settings like shadows/SSAO/sunshafts/lighting and outline mode because the graphics card were especially weak against those). In arena I could almost have everything on ultra 5k res because of the few numbers of players moving around.
In Hereos of Newerth it was even better than that. 5k resolution with ultra on butter smooth 60fps. I couldn't believe my eyes until the game crashed... and it crashed again... so I turned the settings down to high and I didn't receive a weird instant crash like on ultra.
and of course, the fan was barely audible with in-game sounds being muted. The fans were like a soft whisper.
I have officially been spoiled... Full HD looks blurry and dull