Here are the specs of my two gaming rigs:
5960x-4.4|AsusRE5|16g DDR4-2133|EVGA GTX980TI SC-EK Block|2Smsng 850 EVO 500gb ssds Raid0|2Tb WD Blk|Win10-64|PC P&C 1200W|Thrmltake X9|Custom H20 cooling|BenQ BL3200PT
4790k-4.6|AsusMxVIIH|16g DDR3-2133|2Sphr Tri-X R9-290s in CF-EKBlocks|Cru M500-240g ssd:500g WD Blk|Win10-64|PC P&C 950W|HAF932Adv|Custom H20 cooling|Achiva Shimian
As you can see, I have a single gtx980ti sc in the 5960x and 2 290s in the 4790k. The 290s are Sapphire Tri-Xs at 1000 core/1300 mem. Your 390 is a bit faster but my observation is the 980Ti is smoother. Even accounting for the cpu difference, the dual 290s are slightly faster in synthetics and in overall fps but the 980ti "feels" smoother. It's a close call.