Dual as in cards? Its a setting in your graphics settings, not in game. But having 2 always helps.
As for me I have
Os: Windows 7 Home Premium 64 bit
Cpu: Intel core i7, 2.4
Ram: 8GB
GC: Nvidia Evga Classified GTX 590 (dual card in one) has 768-bit (384-bit per GPU), 3,072MB of GDDR5
ANd with updated drivers (it should tell you when you login to GW2 if your drivers work with the game) It runs on max settings all high and ultra, and i even have another program that pushes the textures to 32x anti-aliasing, and the texture depth (lod) up or down (forces bump mapping) and with that today up to date on GW2 updates it runs at a solid 62-58 fps. runs like a dream. Only place i get any drop so far is the "heart of the mist" with 40+ people running around doing all there spells...i drop to 46-39..
---------- Post added 2012-08-21 at 09:24 PM ----------
Yeah for this it might have been the stress test, but it depends one what bate, I had a few problems my self, in some of them they seam to be still tweeking the graphics in-game. So, wait and see, it should fix it self out, it did this last beta for me. But i did notice that they have changed the graphics settings all together, over the past few betas.
Another thing, make sure you don't settle for crap, you should run your card at balanced and you should be fine on high to med settings. And if it runs great one day then turns to crap the next, try a good old fashioned restart, that always gets things running better for me. hope it helped. see you around in game.