I believe you need 42 amps on a single rail. The seasonic you linked is 2 rails, 24 amps each. Even if both 6 pin vga cables are each on separate rails, it'll be cutting it close.
I'd get a single rail PSU. Preferably with 2 x 6+2 pin connectors, as you need two of them for the 770.
ok thats what i was afraid of
. But I've had a GTX 480 which has identical power requirements and everything has been running fine for over a year so im kind of confused at the moment...