I have Corsair 750TX v2.0 for like 6 months and i think it is perfect.
You won't go wrong with either of them, but if you want 2x powerful gpu, than go with 600GS.
It does not have wattage enough for like 2x GTX670.
You will handle a single powerful gpu with the CX though.
My recommendation is CX
Corsair is a very good psu brand, so get which one you think it is best.