I have two 270X's in Crossfire, but they are different brands and BIOS revisions. One is an XFX with 15.041 BIOS and the other is a VisionTek with 15.040 BIOS.
They seem to work well--I'm getting anywhere from 60 to 115fps in Battlefield 4 on Ultra with 2xMSAA at 1080p, but whenever I look at something like the Bellagio-esque water feature out front of the giant Chinese skyscraper in the campaign I get massive FPS dips down into the teens and twenties until I look away.
I'm thinking maybe if they both had the same BIOS they would work better together or is that just wishful thinking? Does it really matter?
ASRock 990FX Extreme3
AMD FX-8320 @ 3.8Ghz
Corsair H60 2013 Edition
16 gb (2x 8gb) PNY XLR8 DDR3 1600Mhz 9-9-9-24
2x AMD Radeon 270X in Crossfire 1150mhz core/1450mhz mem
Toshiba Q Series Pro 128gb SSD (Windows and a handful of games)
Toshiba 5400rpm 320gb HDD (Files and storage)
Windows 8.1 64-bit
No they can't use the same BIOS, as they are two different cards with a different PCBs, if you tried to do that, you would brick one of your cards. Performance problems are usually resolved with either game updates or driver updates. All I can suggest is that you update to the latest drivers and see if it helps your problem. It could also be a Crossfire problem, you can also try turning off Crossfire and see if that fixes the problem.