40 FPS is by my standards underperforming to play with. Technically if your system meets the RECOMMENDED system requirements for Overwatch, should be able to get 60 FPS with at least minimum graphic settings on the Overwatch video options. Now systems that only meet MINIMUM system requirements, or use UNSUPPORTED hardware, may encounter undesirable performance in their games.
That being said, these steps are great starting points to check and update any part of your computer to improve system performance with Overwatch:
In addition, I do have a very extensive guide that you should look through to see advanced steps to get the best possible frame rate and response performance. Which you can find here: