Hi Ed, I'm addicted to both types of props as a result of experimentation. "E" props are the strongest but can break just as easily when used on my belly landing airplanes. The SF props work very well for vertical maneuvers and the more flexible ones can provide some useful "variable pitch" characteristics that can be a lot of fun when flying at various altitudes - no prop pitch changes are needed to compensate for air density changes.
I add carbon fiber "tow material" to the center area of props where there might be a question of strength. The SF props require more work to balance and trim them for "reasonably accurate" tip tracking. I love the SF props not ony for their extra thrust but also the neat sounds in reduced power dives that most of them can produce. My fighter threads show the success I am enjoying with lots of different props under different conditions on different planes. Clicking on "Ratings" on the first page of this forum brings up a lot of different fighters with information about "E" and "SF" props.
Hope this helps.
Out. (a little fighter pilot talk here)
FIGHTERS - AVIATION'S ULTIMATE CALL TO GLORY, HONOR, AND IMMORTALITY - http://community-2.webtv.net/RICHARD...4/CALLTOGLORY/