Low framerate is not necessarily due to too litle RAM, it's mostly related to GPU and CPU. Most games don't use more than 1GB-2GB of RAM anyway during gameplay, the recommended memory amounts have to do with the margin of space the game has to run in, it's very different to have a game that consumes 1GB of RAM running in a 4GB of RAM PC along with Windows and other applications sharing that memory, and the same game running in a 8GB rig. And usually the loading times are the thing that gets more affected by low RAM issues, since the chunks of data being loaded have to be smaller and more controlled, and that takes more time to do than to just load everything onto memory pretty much at once.
Too much RAM is not benefitial either since you end up buying an expensive RAM card just so your rig only uses like half of it.