Did you pull the cards out and make sure all the heatsinks were tight? In Blades, low efficiency is usually due to chips overheating from poor heatsink contact, and these Cubes are notorious for loose screws upon delivery.
Right, I got no more X's and efficiency up to 50% but declining
MHS 04764
I unscrewed both sides of the cube but found it rather tight to push the board out, so I just made sure that the cards were properly slotted in place, they were not screwed to the main board and seemed to be wedged in place by the groves aligned at the top of the cubes structure, I just made sure these lined up correctly and put the device back together.
Any other advice on how I can get the optimum performance from this unit?