Hello. Just now catching this thread. In all honesty, if you can get a r9 290 for 210 dollars I'd go for it. However if you want the better card for 330 dollars and that beats the gtx 970 in most games, then the r9 390 is the way to go.
Get the msi version as it overclocks to 1060mhz by default. I've attached a video of the comparison you requested. The video also contains the gtx 970, r9 290, r9 390x, and the r9 390 of course.
Oh and the R9 390 series actually uses more power as they are clocked higher and have a higher stock voltage.
Same GPUs, just more VRAM.
https://www.youtube.com/watch?v=vSDQzlKDYq4
Generally speaking you're going to get lower temps and power consumption from the r9 390, which essentially means more overclocking potential. (I've managed to get my r9 390 to 1120 mhz for example). Because you can overclock more, you're capitalizing on the already substantial gain in performance you'd get over the r9 290. The r9 390 is the better investment in my opinion.