It will very well depend on the game itself-on paper a 380 crossfire will beat a 970 but you will run into issues such as bad scaling or even none existent crossfire profiles for certain games. Also factor in the increased power draw and heat generation.
I am personally not a fan of multi gpu setups if a single card configuration can achieve similar results.
Tl;dr just go for a 970 or even consider a r9 390