This is probably really old news, but I haven't seen it, and to be honest, I thought this game was GPU-bound, but no :P
Display: the graphics-settings slider has only a minor impact on performance at this time.
We are currently optimizing Guild Wars 2, making ongoing improvements to the game’s frame rate. Presently, the game is CPU-bound on most high-end systems, so lowering graphics settings or upgrading your video card may not have a large impact on performance.
On older or lower-end machines, it is recommended that you try disabling reflections to improve frame rate.
I found it on GW2's forum '' currently known issues''