Doghouse, I have exactly the same problem – and almost the same system: Win7Ultimate 64bit, 8GB RAM, nVidia GeForce GTX 750 Ti.
Normally I have 40-100 fps depending on the area I am, but since the Jan.12. patch, the game often starts in 20-25 fps mode – wherever I am/whatever I do. After several restarts of the game, it will be OK again.
Support says it’s a hardware problem – even though the problem appears only in GW2, only right after the Jan.12, patch. All other games are running with no problems.
Did you find any solution?