Crossfire psu needs?

hello! i am debating on whether or not to add a second amd 7870 to my pc, or whether i should just buy one nvidia gtx 770? problem is i currently have a thermaltake toughpower xt 675w psu and for the life of me i cannot figure out wether this is good enough!? i assume it is not considering i'm everclocking and running a lot in my system. your thoughts will help since i need something more powerful while saving as much money as possible! thanks!

I personally would trust that psu with a 7870 let alone a 770.

I would sell the 7870 while you will still get good $$$ for it and buy a nice psu plus the gtx770.

a 7870 in crossfire can keep up with a 770, so... unless you get a fortune for that 7870 card... I would go for xfire.

but I fear you will need about 700watt to be asured you can pull it off... what is your cpu and other hardware?