All maxed out including supersampling my performance can go as low as 20 in pve, in big events, 27 just running around as lowest, and average can be around 40-50-60 and even 70 in some areas. Even more as max FPS perhaps. In wvw I think I got 16 fps as lowest. I've tested with 3dmark and i get around 9400-9600 points on my gtx 680 superclocked and i5 2500k 4.2 so nothing wrong on my computer, not on my power plan, not wrong drivers.
So what's wrong with it? When I drop my gpu usage drops aswell.