I also disabled the ingame FPS counter, it does not update fast enough to capture this moment in time and used an OSD.
Now I'd like to claim the record with 4009.3 FPS. I know this has no identifier but its impossible to get the highest FPS possible with an identifier. I also did not want to watermark it because I want this to be a legitimate GunZ screenshot.
http://i.imgur.com/56iERGI.jpg
I have a whole FOLDER of high FPS images to prove it's mine. + I made a gallery explaining how I got to that point. If the picture MUST have an identifier, the highest you can go ingame is about 3.4k~ AFAIK and I have one of me doing that.
http://i.imgur.com/05cFKFz.jpg
I've made a album explaining the process at which I got to 4k fps. [Document is namestamped to my imgur account.]
http://imgur.com/a/1n8kv