GTX 670 or HD7970 with 650 watt PSU

Hi,
I'm having a hard time deciding between GTX 670 and HD7970. I'm leaning toward 7970 at the moment due to "Never Settle" bundle. But I'm a bit worry about their power requirement. When calculated using extreme power supply calculator, I'm coming very close to the recommended power requirement (634 watt assuming 100% cpu uti, peak, and 20% aging). While using GTX 670 it's only 575 watt.

My power supply is corsair TX650 v2, it's only 6 month old so I'm not looking to replace it.
My monitor resolution is 1080p with 1 23' pc monitor and 1 40' 3d HDTV (love playing skyrim on the big screen   )

Is it safe for me to go ahead with HD7970 (Gigabyte GV-R797OC-3GD) or should I go with GTX 670? My main concern is that my PSU won't last very long if pushed with higher power requirement and I it won't be enough for the Gigabyte 7970 since it's overclocked edition.
Price are the same in my country but I got free game with AMD.

The rest of the spec:
Asus P8z6 m-pro
i5 2500k (OC to 4300)
2x4 Corsair DDR3 1600
SSD Corsair force gt, 1 wd black, 1 wd green, 1 old HDD, 1 external usb WD My passport
1 external DVD Combo
SB Recon3d PCIE
NZXT fan control, 3 extra fan
xbox controller, razer naga razer black widow ultimate, Logitech k400
Corsair TX650 V2 (650 watt)