Some user had and issue on non-KPE card, after he flashed KPE BIOS, it worked, but once he wanted to revert it back - it got locked out during flashing and BIOS got corrupt. He could not reflash card to anything else, no matter what he tried. He ended up shipping card to me, I replaced BIOS chip and reprogrammed it via hardware, then card restored to functional state. KPE BIOSes have some stuff that configures hardware onboard. If it's flashed to wrong card, it could cause conflict and configure hardware into wrong settings, without option to revert back to default/factory state. So in general I will always recommend to use compatible BIOSes, and not willy nilly flashing whatever binary you may find in the internet. YMMV.
And no matter what BIOS you use , you CANNOT unlock any voltage, there are dozen of limitations from NV drivers and settings to prevent exactly that. Whatever additional voltages possible otherwise - it is means by either hardware stuff (voltmods, special trickery, unofficial rogue hacks) or simply incorrect reporting/monitoring. And going past 1.2V on anything but subzero cooling would often cause you LOWER performance (not clock MHz, these can go higher, but what's the point if your performance does not improve?), because you hit those power limits/thermal limits earlier.