If by "old rubber" you mean cat whiskers, a safe bet is between 3-15 fps, depending on how you installed them, if you did any trimming, how close to the center of the string, what kind of bow you're shooting, how heavy an arrow you are shooting, etc, etc...

How much FPS loss, or specifically transferable energy loss is primarily a matter of how much the object(s) attached to the string weighs and how close they are to the center of the string.

If they weigh 30 grains each, that's 60 total grains. If you are shooting a modern bow near IBO weights, you may well lose more than if you are shooting a much heavier total grain weight "hunting" arrow.

How much drop are you experiencing with your pins? Probably not much, and not worth worrying about, especially if it is on a hunting bow where silence is more desireable, to a point