Buy a custom 290X and outperform both for less cash. AMD drivers have improved the performance of all their 2xx/3xx series cards. An overclocked 290X will beat out a 970/390/390X and stock clocked 980. Best cost to performance ratio for a card in the $300-350 price range right now. 390X is just a rebrand of the 290X with a 50MHz bump on the core clock.
The Sapphire Tri-X 290X preforms and overclocks beautifully. I have several friends that own it and have nothing but great things to say. Card is $329 on Newegg.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814202089&cm_re=290x-_-14-202-089-_-Product