There is no "mod" that makes 1.21V work. All reference boards go up to 1.21V but it is not reported by software, software merely reports what the BIOS tells it to - which is the max offset voltage of 1175mV. So seeing people go crazy over this BIOS is pretty hilarious

IMO because 680s have been doing 1.2V for a long time now, people just didn't realize it because nobody tested their cards with multimeters.
I had EVGA ref cards that would do 1.21 at 100% GPU load, ages ago - verified with a multimeter. But because overclocking is retarded with the kepler, people take the misreported voltage by software and think it means something. By the way, all kepler cards throttle at 70C, they will lower in 1 bin increments (13 mhz / 10mV) which you can see if you watch the monitor in precision x or whatever monitoring software you have.