At a guess, all other things being equal (same boat, trim, load, etc.), which would likely be faster, a '54 10HP Johnson with a replacement 9x7 prop, or a '58 Evinrude 10HP with the original 8.25x8 prop?
If one of the props lets the engine run at the RPM where it is making it's best power, it will produce the highest speed, the other one will have the engine either above or below the power peak and the boat will run slower. However the holeshot may be faster or slower depending on which direction the pitch of the nonoptimal prop went
