I think maybe 600Watts is a little extreme But if you are prepared to pay so much for just a PSU... I suppose... but will you seriously put in another 7800?
I have the enermax noisetaker, 600w 620 peak and it is just about enough for both hd's both gpu's and all the flashy lights and fans and all the extra other bullshit I have. I've never had any other psu than enermax, so I would recommend them, but I just don't know about anything else, not gunna bash what I haven't tried.