Well TBH the power consumption isn't that high compared to last generations cards, Pascal just made a huge leap forward in terms of efficiency. Also undervolting helps with performance and power consumption. Sure it is ~100W more than a GTX 1070, but in my case PC's total consumption goes from 450-> 550 Watts, roughly.
I have a Vega 64 running in custom waterloop but I haven't had much time to play DCS yet. Performance seemed worse than with GTX 1070 with my ~30mins of playing. FPS seemed to drop below 45 everytime I maneuvered, but if I flew straight FPS would go over 90 with VR (Rift) even if I moved my head around. This seemed weird and needs more testing when I have the time. GPU usage seemed to fluctuate between 40-90% with GPU clocks jumping between 400-1200 mostly, where max settings were at 1700 Mhz. Seems like DCS doesn't push the GPU nearly as much as it could be used, compared to GTX 1070 that I had previously. I hope Vega drivers improve in near future and there would be some performance leaps.
DCS is certainly flyable with the Vega, but just not as smooth as it was with a Pascal card. I don't know if my monitor change from 1080p 60Hz to 1440p 144Hz had something to do with performance, as VR copies the image to monitor too. Don't really think it should matter.
I opened another thread for Vega performance as I somehow missed this Hardware section totally. Could have just posted here instead of opening a new one.