R390s are reputed to be best for high resolution gaming modes, versus the Nvidia equivalent GTX-970 which is another badass card for mining - so there
are active fans, VRAM up to 8GB etc to consider, etc... all these will require more wattage.
A fury is much better at 4K plus. It is also more efficient.
There is a altcoins mining thread. Keep that in mind.
king_pin has contributed a lot to this thread. You should look and read through the tread if you don't recognize him (assuming he could be wrong). I interpret his post as a warning to new miners, based on his experience. I can tell you from my own that mining in the summer, or running many rigs in the same room drastically changes how your rig will run.
For pure cost effectiveness a 380 is the best new card to buy. Adding a single configuration setting will allow it to mine ETH at 20mh with stock freqs and the card costs ~$200. At stock freqs a single 380 should use ~170 watts. This is much more efficient than OC'ed 390's.