There's no Vsync off option in FL, it's forced on. You have to override it using GPU drivers, maybe you've set global settings with Vsync off in your GPU control panel, and that overrides FL if you keep hitting 180.
I use an i5 and a HD7950 3 gb card; I'm locked at 60 (because that's the refresh rate of my screen), unless I force Vsync off in my GPU control panel. Without Vsync I easily run at 180 too, but I have to forcefully override FL to achieve that.
Check your Nvidia Control Panel for global settings; Nvidia cards can override FL very easily without having to use extra tools like you do on ATI cards.
