I did some cycle touring up round there in 2016 - did some big days out around the west coast. The bits that were on NC500 were often quite busy (this was in September, I imagine it's worse in July / August) and it was often "convoys" - things like 3 or 4 MX5s, a couple of sports cars, a trio of camper vans. Get 3 camper vans coming one way and a minibus going the other and nothing is getting past anything for ages. I can see why some people would get annoyed at it.
The bits that I did away from the NC500 route were noticeably quieter although "quiet" is a relative term; all the roads were quiet just with a couple of busy moments.
Lookrider wrote:Do you know the altnaharra area enough to recommend somewhere for food. ..we are staying overnight at the altnaharra hotel but it appears they are exploiting the cyclists on the 500 and charging an awful lot of money for not a lot of food
Altnaharra is nowhere near the NC500. It is however on LEJOG / JOGLE routes - if you're avoiding the A9 up the east coast then the route through the middle is the obvious alternative. Crask Inn, Altnaharra, and then either Tongue or Bettyhill. That's your lot for food. Can stop at Bonar Bridge or Lairg on the way up. And they're not "exploiting" cyclists. They're charging what they have to do in order to survive a 12-month year on probably 4-5 months of passing trade.
One thing that the NC500 has done is move all the trade out to that area so a cafe or B&B on the route will do roaring trade but one literally a couple of miles away won't get anyone passing by because they've all been lured off to the NC500.