The gross weight increase offered by the VG STC is a direct
result of the reduction in stall speed. Under the FARs, light twins are required to have an engine-out rate-of-climb (in feet/minute) equal to .027 times the square of Vso (in knots). If you lower Vso by a few knots, the required single-engine ROC goes down. At the same time,
That requirement is outdated, from CAR 3. The current Part 23 climb requirement is not related to the stall speed.