The same config with 16 cards + without oc work well. so i don't think that there is trouble with intesivity.
Remember also.
nVidia themselves have put on a hardcap of max GPU in their drivers for 'gaming' GPU's in one machine.
Seeing you have under the 16 'gaming' GPU and mining GPU also, this shouldn't be an issue.
We are about to build a few of these this coming week, with ALL 'gaming' GPU's, so I think we will cap our systems at 16 GPU for every miner.
We will be mining under the CWI name, so look out for that sort of performance when it comes about, as we will be testing both ccminer-tpruvot and CWIgm-0.9.9
#crysx