Also IMO they wasted the 3'd PCI-E connector on each board, even 2 per board would have given plenty of overhead for significant overclock (with the lower voltage per chip these aren't going to overclock as high on average as an S5 anyway).
I suppose their thinking for a 3rd PCI-E connector is when / if you used (cheap) PSU's with say 18AWG cables, you'd be able to make it up with the third.