You might notice lot of game streamer has a display offps, temperature and also ram usage shown in top left part of the screen. It actually help to notice the performance of your hardware. And for the future, you can change the hardware like graphic card and compare the improvement.
The software they usually use is MSI afterburner. This software is developed by Guru3D and MSI. This software is basically use for overclocking and under clocking the graphic card. It can be further use for maintaining the GPU temperature.
First download the MSI afterburner stable version from here. Then open it and go to properties. Open monitoring tab and select which meter you want software to show.
Then go to on-screen display setting. select the keys to Toggle on-screen display like ALT + O
Start the game and press ALT + O to display the monitor.
Full FPS and temperature monitor video tutorial