The Witcher 3 was a classic example of this, with its astonishing clarity traded up against a slow but playable frame rate.
I've been playing the Witcher 3 on a 1440p GSYNC-capable monitor (Asus ROG Swift) and a GeForce 970 and although technically the framerate hovers around 45-55, it is incredibly smooth thanks to the GSYNC framerate matching. It looks as if it's more like the high 80s. Maybe full 4K gaming should wait until either GSYNC or FreeSync (the AMD version) is supported.
As for StarTech - never again. I bought one of their HDMI-DisplayPort active converters. It burned out in less than an hour.