Jason, I would try a 10 x 4 prop on that O.S. 40 FP engine on your Stamp/PBF, which is better for hovering and slow speed flight at which this plane excels. A 10 x 6 prop will make this plane fly too fast at full throttle, which will lead to that flexing at the tips, and it will not respond to throttle changes as quickly as the 10 x 4.
I'm using a hollow carbon fiber arrow shaft across the leading edge that's zip-tied in about six places, and it has stopped the flexing at higher speeds. It is very light, and I haven't broken one yet. :-)