You can modify the bios on the 380x but the main issue is the 256bit Memory bus. The 390s have 512bit Memory bus. Overall Tonga (380s) are weak for ZEC. That being said you should use your 380s for ETH because you can get between 22MH/s and 24MH/s. Currently I have a Powercolor R9 380 running at 24.7MH/s on ETH. Also one reason some cards do better than others of the same model is the memory type the cards have. Samsung and Hynix are excellent for overclocking, Elpida not soo much.