I have done an experiment to try to find out if in such a low-noise sensor as the K5's, those 14 bits are really useful or just marketing like in most 14-bit cameras. I asked Manuel Llorens
to compile a version of DCRAW allowing the user to discard the N least significant bits prior to demosaicing, and used it on the well known 6-stops underexposed DNG file from the K5:
It's difficult to see any loss from 14 to 13 bits, but using 12 bits visible posterization begins:
So the conclusion is that K5's sensor at ISO80 has such a low level of noise that can actually benefit from using 14-bit RAW files instead of staying at 12-bit, that would suffice most present 14-bit cameras.