Awesome info, thank you!No, the GTX 660 OEM is on GK104 too. Only the GTX 660 retail is on GK 106.
nVidia is not really communicating about it, but here is an extract from a Tom's hardware back in September :
Edit : and yes, it's not really a fantastic card for AA and very high-res (which matters less for X51, most than probably destined to be hooked on a Television capped at 1080p and played from a greater distance anyway).
Good point about not really needing AA on a TV set, I hadn't considered that.