Gentlemen,

The two versions you mention are well outside "the sweet spot". I suspect you are well aware of this. ;-)

Super-narrow slicks on a mountain bike will ride as harshly as they do on a road bike. Fat, knobby tires on a road bike will be as rough, noisy and sluggish as they are on a mountain bike or beach cruiser when ridden on a paved surface. Those versions are outside the desired envelope.

What's being suggested is to use fat, high pressure slicks (or lightly treaded) tires on a zippy frame. Because most road frames will not accept fat enough tires, many have opted for smaller diameter wheels. What this does is move the point of maximum tire width (not tire height) to a smaller diameter, thereby gaining additional clearance from the frame.

What would be cool is to compile a list of bikes which are available set up this way. Another cool list would be of frames compatible with this set up.