Looking to go Crossfire on R9 390 Wattage recommendation?

[Keoninzmu]

I was considering going crossfire on two R9 390's but when i poked around to see what wattage I should get for the power supply i saw varying things. I'm not planning at any time to overclock my Cpu or Gpu's, people on the internet were buying 1000W Power supply's but when i used a psu calculator it said that it would use 740ish watts. I know that there is a fudge factor and i know that you are supposed to have about 20% of the power not being used but i am cheap and i do know how stupid it is to cheap out on the psu, at this time i am just looking.

Hardware
i7-6700 stock
2x R9 390
Corsair Cx750m

I know there is gripe about this Corsair power supply and its cheap soldering but i figured that since this is the updated model and people seemed to get it anyways it should be alright. I leave my computer on for normally 8 hours a day but sometimes 2 or 3 days.

 

[ak47jar3d]

A good 850 watt power supply will do in my opinion without any overclocks.

 

[Clamyboy74]

Corsair's CX series (old model with green) have a 750 wattage rating at 30 degrees Celsius. Since 30 degrees Celsius is pretty low for a power supply, the moment you get over 30, the rated wattage decreases (I don't know how much). I would NOT recommend going crossfire with a cx 750 unless your room temps are very low, or you have a giant fan helping to cool the power supply
http://www.corsair.com/en-us/cx750-80-plus-bronze-certified-power-supply
Look at the continuous output rated temperature on the chart
Edit: link leads to cx series, but Cx and cxm series are the same internally, they both have the same specs except for the modularity