I had similar happening. I played some other games that have reccomended requirements higher than GW2, and never had problems. I have a Geforce gt 560.
I followed what someone said about downclocking, and it worked. Then someone in my guild said they got the beta driver and it fixed, and indeed once I was gonna lunch the game and I got a warning saying my driver should be updated, I couldn’t find any update because it was beta. So now, I isntanlled the 306.02 beta, and moved back to perfomance > quality, and my freezing stopped. Have you tried it?