Taken from exedy website.......
All Exedy racing and performance clutches are not modified or rebuilt from stock clutches like other racing clutch suppliers. When a stock clutch is modified, the life span of the clutch is reduced dramatically due to change of higher torque capacity and clamp load that a stock clutch was not designed for. All Exedy racing and performance clutches are designed, engineered, and built as race clutches.

ACT is a rebuild but I won't doubt it's capability due to the good reviews it gets. Also price was a factor. $260 Exedy vs $360 ACT