Regarding repetition spring regulation on grand pianos, I use the standard
given in a Yamaha service manual:

  "There should be enough tension to raise the hammer to the point where
  the repetition lever touches the drop screw.  If the hammer rises so
  fast as to create a "bump" that can be felt in the key, too much
  tension is present."

While you can't always achieve this standard on older pianos, it is a
good ideal to strive for.  It makes sense because the pianist wouldn't
want to feel the "bump", but you want that lever to rise as fast and as
far as possible for the quickest response to a repeat keystroke.