Thinking another GTX 460 would be the best bet. Just thinking if the PSU will handle it. I'm going to overclock the CPU once I get a heatsink(using stock cooler).
The HX one has a higher effiency rating. I am pretty sure the 12v rail is more on the HX one as well. I have a HX750 and they are solid as you like and i sure the guys here will echo my view.
I would go for the HX850 in a heart beat.
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