We don't need a delta to determine how big a fraction of each frame is spent in a given API. If profilers show that 0.0001% of the time is spent in a "backwards compatible" API, while 20% of the time is spent in the pathfinder, then the pathfinder is surely a more worthwhile optimization target.
Yeah, svn is pretty old-fashioned. Perhaps we should try to attract more developers by starting a few topics at leading technology forums. (I could start a topic at the dutch site Tweakers.net)