your sonic boom theory has been proven. on my grandpa's Airboat, which had a Lycoming 6 cylinder engine, and an 8 foot propeller, a 4 barrel updraft carburetor, with 6 equal length runners all 4 feet long for an intake, and a tuned exhaust that was directed into the prop for a "free supercharge" by design, showed me why an aircraft needs a gear reduction unit to run the prop at 1800 RPM's or so....
at the speed of sound, the propeller STOPS PRODUCING THRUST. this is wierd, but this is the speed of sound at the propeller tips, apparantly this has something to do with pressure, and viscosity with the oscillations that occur at that speed.
One would typically think it to be the other way around though.....
as for the speed of acceleration:
Look up: Ion Drive Propulsion Units and Plasma Drive Propulsion Units.
both developed by NASA, and for use in space whenever they get around to going someplace other than the moon with people onboard.
AlaskaStar