For the ZEC mining, you do not need the special bios for 7970. There is very little difference.
Not massive differences no, but some. There's a whole thread dedicated to ZEC BIOSes for Tahiti cards with modified memory straps which give better speeds:
https://bitcointalk.org/index.php?topic=1676474.0Unless there's a way to hit ~290 H/s without a BIOS mod? 290-310 looks to be about the max for the 7970/280x cards.
claynore the v12.5 has some issues with auto fans speed on MSI AB 4.3 with Sapphire R9 290 TriFan,using win8.1 64bit Catalyst16.8.2, the fan speed goes from 70% to 40% while mining, so I wonder if you could do anything for this?
Are the fan issues present in v12.4? Don't think 12.5 gave any noticeable increase in speed so if it fixes the fan issue I'd use it instead. Moreover, I've always heard that Catalyst 15.12 is best for the R9 series when mining ZEC, have you tried using them instead?
https://www.guru3d.com/files-details/amd-radeon-software-crimson-15-12-driver-download.html