Going the long, wrong way lol
Trust me you'll be dead by Dent its a long haul
I trided Strontian in one go, Almost never made it , it was a very long way to go for a BBQ lol ( but bloody worth it)
Easier way & route (and i'm on the south coast too)
M27, A34 ,M40/42, M6 - Dent - I stay overnight here, it breaks the trip up
then M6, A74m ,M73,M80, A90 A96 Posrtsoy In one hit 10:50
in 2 hits 5:50 per hit
Lot of big boring roads there, one alternative after Dent would be to meander through the Borders, head for Blairgowrie then smaller roads to Portsoy over the Lecht. Plenty choices.