> My understanding is A roads in the UK are much like USA interstates.

Not in Scotland, some of them aren't dualled (just a single carriageway in each direction), narrow, windey, full of terrible potholes and animals you can hit etc... its a 5-6 hour drive in reality

source: Live in Edinburgh

The A9 is actually pretty scary in parts because it alternates between dual carriageway and single carriageway and people have been known to get that wrong and thing they are on a dual carriageway when it is a single carriageway...

Both Apple and Google Maps greatly underestimate travel times on anything other than perfectly straight motorways. If you've never driven here before you can at least double their estimate, easily - and that assumes you are at least reasonably proficient at driving on the left at all.

The A9 is the most dangerous road in Europe, and you'll be doing 50mph at most along that because there's nowhere to overtake and that's the maximum speed trucks can go at, so you'll end up in a queue behind a truck.

Depending on the route you take, you might go through Inverness, in which case once you get off the A9 most of the road you'll be on looks like this, for about 120 miles: https://maps.app.goo.gl/9L5cSejT1eyAVR2E7

Once you get to Dalwhinnie you can turn off the A9 and start heading across to the A82, which is really pretty especially in the snow but will be mostly road like this: https://maps.app.goo.gl/qv1L21jk59EEAHZs9

Notice how it's not actually wide enough for two cars? But that's still a 60mph road, although you'd be lucky to be getting up to more than about 50mph.

And you'll be driving on the wrong side of the road, in an unfamiliar car, with a manual gearbox.

Good luck.

Google Maps says between 5 and 6 hours and 227 miles - doing that in 3.5 hours would be averaging 65mph. Good luck with that, especially when the speed limit on the A9 itself is 60 mph for cars!

The US interstate is probably more comparable with UK motorways.