Computer games can be very demanding on a personal computer; almost everything is running as fast as it can, in order to provide an enjoyable frame rate while the game is being played. Tom's Hardware has done a comparison of 10 popular games running on the same hardware on Windows 7 and Windows 8. It's a detailed article as usual from the site, but the upshot is that everything is fine. The games generally run as well on one platform as the other. Additionally, as Microsoft has previously indicated, an unusually large patch collection is available now, and this will make some significant changes to the OS - so this may even help a little more.