Personally, I never fly above 20% expo on the radio. You also need to look at the plane's values. One of the planes I looked at had no expo values. One of my favorites.
I'm with 12oclockhigh on this one. Don't like a lot of expo and I have removed it from several of the planes I fly the most. I guess I flew too many years without it and never felt the need...probably why I'm such a bad pilot. LOL
Expo has a role, and high expo has a role as well. It's completely dependent on how you fly and what you fly. When used properly, it keeps the plane controllable while still allowing rapid and extreme control throws. I have used expo as high as 80% for some routines on planes that required 60-80 degree control throws for particular maneuvers with much less extreme maneuvers before and after. Normally, I would switch to very high rates and back just for that maneuver, but if the routine flows in and out, that isn't always possible.
As a general rule, I use 15-20% for low rates, because somewhere in that range is necessary to produce true linear movement of the control surface from a rotating servo horn. For high rates I start with the greater of 20% or half of the control surface throw in degrees, then adjust as necessary for the flying I do with that plane.
Interesting. I don't think I've ever seen a general rule of thumb regarding Expo setup. Don't recall ever looking for one actually. But, I'm going to experiment with those percentages. Maybe it will help me.
So are these extreme maneuvers related to 3D flying?