I’ve found I can cap the TDP on several games without any noticeable change in performance. The important part is to remember that you set a cap if you start getting FPS drops in another part of the game.

There are also some games that have bugged cpu or gpu clock speed, where the game will run one at max clock speed unnecessarily causing extra power drain and performance issues (for example the CPU may be using too much power and staving the GPU, even though the CPU doesn’t need to be running at max speed). For capping cpu you have to use the decky plugin power tools or another method.

Checking on ProtonDB is a good place to look for recommended performance tweaks, looks like a lot of reviews there mention capping Cassette Beasts at 10 TDP, and a couple more mention capping the GPU speed at 800.