Just as an experiment try turning the half hashers down to 300 mhz and see if that makes a difference.  Mine run anywhere from 42C to 48C and still drop to half rate if I go over 352 mhz.  Zipiju thinks it is most likely a power issue with the components on my boards.  He said that each bank of chips has it's own hardware to regulate power.  If the K16 hashes at half rate it is likely that it is only functioning on one bank of chips.

Just something to try...if you get a good average 4.5 gigahashes at 300 mhz that is the likely culprit.  If they work fine at 300 you can start bumping it up 1 mhz at a time until you find the point that a bank drops out or hardware errors start going nuts.

My two K16's have been running 24/7 flawlessly at 352 mhz on a Raspberry Pi for more than a week now.  Other than when I was initially setting them up and messing around with everything the only time they have stopped hashing was for about ten seconds to upgrade from cgminer 3.8.1 to 3.8.2.

Good luck!

Chad