You have to make a cost arbitrage.
No disrespect, but Cost arbitrage?? is that a thing?
Comparing two costs and the return from each is part of a investment return, not really arbitrage... just saying....
Because running 3 cards instead of 6 will cost you $10 a day.
I'm not following that, how does that work?
I use two PSUs on a couple of rigs. I've found that if I use a good 750-900w Gold PSU to run my board and a couple GPUs, then a cheaper (still bronze or gold) PSU for the remaining PSUs, along with a PSU cable splitter, - works great and it's less costly than a overly priced 1000-1200w PSU.