JT,
Underpowered is another word for over gross, I guess. We used 2.3% as minimum gradient a significant reduction from the FAR 25 3.0% for quads. Being a quad, AEO take-off run was quite close to OEI BFL, so one saw a lot of runway. The 115% rule provided some protection. That said, climb gradient and obstacle clearance tended to be more restrictive than runway performance, so take-offs didn't usually dust off the overrun.