"Supposedly" their efficiency only starts to kick in when they're 50% under load. Some actually are advising running two PSUs instead of just 1 "if" you are starting out with 2/3 outta 6.
Another difference is between Gold and Platinum. I see quite a few say that their is little difference, or "not" much different between the 2. 2% worth the plat between the gold?
Any thoughts?
Keep in mind that you will definitely lose money by upgrading later if you choose to slowly ramp up to a larger mining farm.
So find out how many mining rigs you would need to use to make the 2.2% decrease in electricity cost negate the increased costs of the PSUs and then decide if that amount of rigs is something that you would like to own in the future.