There's a guy back in Illinois named Art Mattson who has done a bunch of speed mod stc's for Cherokee's (wingtips, VG's, stab tips, etc) but he also has an stc for modifying the tips on a Sensenich 74DM series prop. What he does is to undercut the tips, sort of along the lines of a Hoerner style wingtip. His description of the benefit boils down to you can pitch the propeller up 2" for more cruise without losing any climb. I guess that means it can turn up to the same rpm as before,due to increased efficiently. He has a website, pipermods.com, and here's a link to the prop-mod page: www.pipermods.com/proptip.html
You can even buy a new prop, through him of course, and Sensenich will do the tip mod at the factory. Comparing him to other prop sources, his price is such that the tip mod is just about thrown in free with the prop purchase.
My question is, does anyone have any personal (or almost personal) experience with this mod? It soulds like a win/win situation, and the best thing since sliced bread- but you know how that goes.

Eric

Over at AOPA/forums there has been a lot of discussion about this mod. I think you will find some good info/feedback over there.