Important Update: there will be no LN2 bios and no Afterburner Extreme for the GTX 750.
The reason is that the procedure to make 40 LN2 BIOSes (that's how many models there are worldwide) is too much work and the LN2 bios only increases the power limit slightly anyway. It should be possible to max out the card even without the special LN2 bios. For the Afterburner, it comes down to the PWM IC used for the GTX 750 doesn't support voltage control. So even with a special version, there wouldn't be any gain voltage wise
So yeah ... go crazy on the PWM modding!