As stated, there are no video sources with HDMI 2.0 outputs. The way the GPUs work is that, the R9 295x2 for example, detects what input is being used on the display and adjusts its output signal to match -- the signal is not converted. If connected to HDMI, it will output an HDMI signal.
The firmware on GPUs does not currently support HDMI 2.0 out - it detects its transmitting to an HDMI, and the best it can do is HDMI 1.4a despite its mDP 1.2 being able to handle the same load as HDMI 2.0 - it doesn't recognize that the interface has changed.
Hopefully the drivers will be updated, but that is a work in progress. Currently you will cap at 24-30 Hz at 4k using an HDMI input on a display, regardless of the capabilities of the A/V source. The only way this is not the case is via streamed content through a Smart device, or a receiver with an HDMI 2.0 output.