Nvidia has updated its drivers with the release of WHQL stamped Geforce 275.33 driver. The new driver is pretty much what you've seen with the 275.27 Beta except for the Witcher 2 performance-drop issue that is now fixed.
Same as the 275.33 Beta, the new Geforce 275.33 WHQL driver has a handful of performance improvements for the GTX 580 and the GTX 560 including games like Crysis 2, Civilization V, Portal 2, Bulletstorm and Batman: Arkham Asylum. The most noticeable improvements are in Batman: Arkham Asylum with Physx set at high and in Bulletstorm title with enabled Antialiasing, where the perfromance improvement goes up to 15 percent.
In case you are already running the 275.33 Beta, you might want to switch to WHQL version if you are planning on giving the Witcher 2 a try, as the sudden perfromance drop issue is now fixed.
You can download the new driver here.