It depends on how tight the nock fits the string. You'd really have to shoot through a chronograph and do the numbers crunching to figure out how much energy tight fitting nocks cause. I've seen as much as 25 fps difference between an extremely tight nock and one that fits properly.

Another item that can drastically affect arrow speed is how clean your release is. A clean release can get an additional 10-15 fps. Even more if you use a static hold at anchor that you let creep forward at release and switch to a dynamic pull-through, back tension release.