I bit of thoughtful signage wouldn't go a miss on the A9. It would be useful to have a countdown to the dual carriageway sections. I'm sick of seeing suicidal overtaking moves when then next dual carriageway is only a few moments away. By the same measure it would be useful to know how long the dual carriageways are going to last, some are pretty long but some are over in the blink of an eye, and either way you only get a 400 yard warning that they are about to end, given the trucks can running nose to tail 400 yds isn't much time to find a space amongst them.
On balance though there's no reward for being in a hurry on that road, passing one vehicle just puts you behind another one around the corner going at the same speed and the effect on your total journey time is negligible. Take the time and enjoy the view.
Its one of the few A roads where I see trucks routinely observe their speed limit on single carriageways, thats why the crawl along at 40 then gun it along the dual carriageways. I wonder whether this observance is the result of truck's getting more attention from the fuzz on that stretch