With V-Sync enabled, the client experience tremendous FPS drops, both in the menus and during gameplay. This occurs both with the in-game V-Sync as well as Nvidia's hardware-side V-sync. This issue DID NOT exist prior to updating to client version 1.9.

I first discovered this when trying to mess with the settings. After turning the in-game V-Sync off, the FPS drop/lag immediately stopped. I decided to further test it by keeping the in-game setting off while turning on V-Sync in the Nvidia Control Panel, to which I experienced the very same FPS drop/lag both in the game menus and during actual gameplay.

The stuttering makes the game completely unplayable, and navigating menus extremely difficult. Clicking options sometimes takes upwards of 10 seconds for a mouse click to register. MSI Afterburner reads the OpenGL framerate as 0.0 FPS. I have no idea if this is involved with AMD based cards as well or only Nvidia. All Nvidia drivers are up-to-date as of 3/2/2016.