With Rivatuner Statistics Server you can lock your framerate to 30FPS. It should help to keep your GPD Win cooler and lower power consumption (longer battery time). It does it's job on the GPD Win when you're playing PC games that can't run at 60fps with VSync enabled.
Rivatuner Statistics Server can be downloaded here: http://www.guru3d.com/files-details/rtss-rivatuner-statistics-server-download.html
I've tried stable version 6.6.0 with Prince Of Persia - The Sands of Time because VSync is broken with this game. It now runs at a stable 30FPS and my GPD Win is a lot cooler when playing the game.
It's also possible to show the FPS on the screen but you've got to enable it because it isn't by default.