PSU needed for 3 x HD 7970

[bublus7]

I guess the figures are accurate.
And yes, more ram should be the reason for different power requirements.

[BloodOnSunday]

850-1000W

[fforforest]

Around 1000w should be OK. Preferably Gold certified.

[thegamekind]

850 is enough and i would use corsair just  preference   

[PenguinWriter]

You could also just get a lower wattage Gold (which are usually cheaper) and buy a PSU adapter so both power supplies turn on at the same time. Else for 3x 7970s I'd suggest at least a 1400W Gold to give you some headroom since most PSUs are not rated for their 100% capacity for more than a few seconds.

[powerlevel]

1200W should be safe.

[Alexander The Great]

Corsair has great products