For what it's worth, I use Windows a lot and Linux almost never. I don't watch CPU usage that closely, but for me, SciTE and Geany are quite fast. I especially like SciTE because I don't normally use IDE-like features anyway and SciTE has always been small and fast on even the wimpiest Windows machine. The times that I've used Geany, it felt fine to me.
The point of my reply is simply that if there are problems with Scintilla, SciTE, or Geany, my guess is that they are absent or not as severe on Windows.
John