I would use the E props up to 5 inches in diameter. If one threw a blade, it wouldn't be the first time a prop let go. As far as I know, the 4.2x4 and 4.75x4.75 that I have been running for a couple of years are E props. The 4.2x4 has seen 42,000 on the G&Z, and the APC safety margin is 190,000 divided by diameter on their sport props. I'm sure that they have tested their props to the point of failure on a test motor, but I doubt if they have a CYCLON set up in the back to really see if those E props will blow on nitro power?