EVERY situation is unique, there is no "magic number" to use as a general rule. I've been past 40 degrees 3 times, and beyond 35 many more. I've also been in situations where I've been under 30 degrees but very close to rolling because a front tire was low and the opposite right tire was high. If the other front tire didn't come down soon, it would have been a different story.

Never trust your clinometer to tell you what's safe and what isn't.

Brent