They have some effect depending on your system and rendering settings. However, complicated systems simulation can have a big effect as well. They STMA PC-12, which uses the SASL plugin, takes a big bite out of fps, as does the x737, which uses its own code. If you read back in the thread you will see that Philip has specifically written the code for the CRJ to spawn multiple threads on multiple cores, which, as far as I know, if a first for a plane for X-Plane. Other than what has been posted by Javier (pretty much a direct correlation between core count and frame rate) we won't have any idea how the CRJ will perform until it ships.