If you only want recording, get any CPU that is capable to play your game and get an Nvidia graphics card capable of nvenc. Choose simple output mode. Use "Hardware (nvenc)" as encoder with "Indistinguishable Quality" as quality. You will not be able to distinguish recordings from the original while having almost no CPU impact. In case of problems, limit the fps of the game to 60 with vsync on, and most games have in-game fps limiters.