Also, all other factors being equal (including the cyclist on the saddle--), is a men's bike with horizontal top tube faster than a women's step-through bike?
Not in any significant degree if all other factors are equal.
The standard diamond frame is stronger than the step-through frame, however. So the step-through frame is likely to be heavier to compensate. Not that weight on a bicycle means very much unless 1) you're carrying it or 2) you're going up hills (though a few pounds aren't going to mean more than a few % difference in your speed) or 3) it's a race and a tiny fraction of a second may make the difference between winning or losing.
Geometry does matter, however -- it changes how the motor (i.e. you) is situated and therefore your air resistance. For an extreme change, think of a utility bike vs. a recumbent racer. But the existence or non-existence of that top bar doesn't matter, as long as the rest is unchanged.