Two thoughts I’d add
1. Lets not forget that thrust decreases with speed increase, both for a jet engine, but especially for thrust produced by a propellor. Hence while deploying even a small amount of flap or slat would increase drag for a properly designed aircraft, it seems plausible to me that if now flying slower at the new minimum drag speed, this could mean that there is more excessive thrust. Hence, a better possible gradient than with flaps/slats up.
2. No one has mentioned the slip stream effect of a propellor over the wing. While non existent for a jet propelled aircraft, this added “wind” over the wing produces extra lift. Quantifying just what this does to values of Vx and Vy I’ll leave to the experts.
Hawk