I just went to the garage and with the bike on the stand, the stand side of the frame is 4.25 inches off the deck.

 

I can't be sure about the N, but on my R, the frame tubeisn't the lowest point. There is some stuff between the tubes that hangs down another inch or so, directly under the engine. But even at that, should still be about the same as you measured.

 

I don't know about your model year but mine came with a ton of ground clearence. My Craftsman floor jack only goes down to 5" and it fits under the
bike at the loest point with room to spare. I have lowered my about just under 2". It has been my main objective to get the thing down.
One of the big gripes aboout the Sportster is the top heavyness at slow speeds. As I have lowered the bike it has became much more stable,
to say nothing of looking much better to me.

Now if you'er into HIGH speed turns that is a differant story.

Prspect Ric

 

Ric,
I bet you REALLY get more stable going over a 2" speed bump?