If you've not done it already, factor in the forest drive at Kielder 13 miles on gravel (ok for any roadbike), either to or from the A68. If you do it from A68 to Kielder you can take the borders roads back up towards Jedburgh and re-join the A68
You're doing quite well but I suggest this amendment and you can miss out even more of the A9 and take in Dava moor, Cawdor and Culloden.
Ammended to avoid the A9 by going via Furness and Culloden Moor. Not a clue where they are, but the roads look better than I imagine sitting on the A9 would be, Day 1 sorted then. Newcastle - Kielder - Peebles - Breamar - Tomitoul - Ferness - Culloden Moor - Dingwall.
You'll love it. Look out for the "Jesus Saves" rock on Dava moor. And this is the view looking towards the Summer Isles on the road from Lochinver to Ullapool via Inverpolly.
Good move, avoid the A9 between Inverness and the Firth of Forth. 70 odd miles of average speed cameras
OK, Day 2 Dingwall - Glenmorangie Distillery - Thurmester - John o' Groats - Thurso (Rock Rose Gin distillery) - Berryhill - Smoo Cave - Drumbeg. Anything I should avoid or something I've missed that I have to see? Nice roads up in that there Scotland.
I've just gotten back from doing the nc500 clockwise on my gs with the mrs. We did Durness to Inverness on one of the days.. the east coast was pretty boring in comparison to the west coast. Factor in some of the roads on your 2nd day are single track with passing places. It can be quite stop and start in places so difficult to maintain a good average speed which obviously increases journey time. Then there's the random highland cattle sat in the middle of the road at times also causing delays. Finally... you'll want to go slow at times just to take in the scenery as it's bloody amazing so factor that in also. It's easy to add an hour or 2 extra in to what the expected journey times are. Loved it though. Mrs even managed southampton to fort William on our day 1. The gs adventure is just a mile muncher! Did feel slightly envious of some of the locals on their sportsbike in some of the twisties though!
If you have the time here is another suggestion. Take the Struie road from the A9 just after Evanton to Bonar Bridge, rejoining the A9 a few miles north of the Dornoch Firth. A few miles further but the road is great on a bike and the view looking over the upper reaches of the firth is fantastic.