The GTX 660 ti is on the same preformance level as the GTX 295, 480, 570, 580, 7870.
Yours is 3gb and the normal 660 ti is 2gb so you should be aproaching the 670.
Here is the GW2 GPU results at 1920x1080at best appearence setting:
Take the GTX670 and GTX580 as reference.Your card should be between them achieving minimum fps of 47,5 and average ~66.9 fps.
The CPU is limiting your gaming on GW2 as it is CPU dependant so OC the CPU will improve preformance.
You can read the analisys of GW2 gaming here:http://www.tomshardware.co.uk/guild-wars-2-performance-benchmark,review-32511.html