Using Pocket Knife creates lag in Guild Wars 2.
Since Pocket Knife is on top of Guild Wars 2's interface using Overwolf, performance issues may appear such like lag or fps drops.
But there are some tricks to improve the Performance:
1. You can activate Windows Aero
2. Play Guild Wars 2 in fullscreen
There is also an Blogpost on Overwolf.
Pocket Knife will also be improved in terms of performance so if you have any suggestions you can send these or help us directly.