Join a empty multiplayer server and check that your FPS is limited by the server(low CPU/GPU usage) raising draw distance can help with this.
Kavala is a good place to test as you can follow the main road going N/S through the town and there are quite a few active lights along the way/side roads that you can fire at.
Pick a spot near town that you set a waypoint to for getting a "before and after" point, screenshot or just remember what kind of FPS you are getting when standing there.
Walk/drive along the road and disable any and all lights you come across at least untill you get to the center of town before going back to your waypoint and compare FPS with what you had before, should be slightly higher wich means for some reason the server is now able to run sliiiightly faster than before.