Speaking strictly theoretically, about only the physics involved, each tenth of a grain reduction in powder will of course lower the 1. recoil, 2. noise and 3. velocity. BUT there comes a point with some powders where, at low load levels you get tremendous pressure spikes. That point is mostly unknown and totally unknown for unknown powders. For example, a friend just had that level of curiosity and using a 357 Magnum revolver, loaded .38 Special cases starting at +P+ with Bullseye powder and worked the load by tenths down to 7/10th of a grain total load at which point the cylinder jammed as there wasn't sufficient velocity for the bullet to clear the cylinder. As he suspected, Bullseye was not a low level spiker.
He has never repeated the experiment with any other powder.

Stu