I'm also choosing between these 3 units.
All the opinions that are given are based on internet review.
Mainly from JohnnyGuru.
Personally I'll be going for the 1250w for the extra wattage.
My reason is that I'm on 3x GTX480
Getting the extra just incase the performance drops when aged.
My old PSU was Corsair HX1000(silver), it's been loyal to me over 5 years & one day after a long holiday it finally can't serve me anymore
1000w is enough to power GTX480 for over 5 years what would ask for!!!
Highly recommend to get the Seasonic Platinum 1000w in your case
Your rig shows that U've only got 1 VGA.
If U wanna go for 2x or 3x VGA surely it could still handell it. My old 1000w silver grade PSU handled it well .
As U said it the makers of Proc & VGA are cutting down on the demand of power.
Remember that 1000w goes much easier on ur power than the 1250.
In short 2x VGA = Seasonic P1000 Platinum 1000w, 3x VGA = Seasonic X1250 Gold 1250w
I've asked the same question, all advice Seasonic over Corsair