If you bought your computer just to mine BTC with GPUs then I would say to return it. It will never pay for itself. Ever.
+1Also switching to mining with 1 card is a terrible idea. Your hash/watt ratio will only get worse.
Well if its his main system that part doesn't matter, if its a mining rig thats a different story.
Sorry I forget about Mining Rig Watt overhead,because my (Super Secrets stuff) setups are very low footprint ~35-31 Watts per Rig
(MB/Ram/OS) not including card.But if the system its a 8 core 10 drives etc pulling 200 watts for a baseline then thats a different story.
But if the OP has $.06 KwH power its not going to effect him as much as $.26 KwH Or Free Power.