850watt PSU for 2x5970's

Hello,

I have come across a second 5970 to add to my current configuration and am not sure if my PSU will be able to handle it. Upgrading is an option but if i can I'd like to avoid it. Any Advice Appreciated

I currently run this configuration,

i7 2600k
Asus z68 pro mobo
8gb coirsoir dominator
128gb crucial m4 ssd
750gb western digital black
ati radeon 5970
850w thermaltake psu
silverstone raven rv02 case