I have been to both countries over 10 years ago. I returned to Scotland with my friends for a long week-end and here is what we did with a car.
Arrive in the afternoon or evening in Edinburgh
Edinburgh - visit the Castle, walk to Carlton Hill & Arthur seat, chill out in the Princes St Gardens, enjoy some Belhaven "Best" and haggis in a pub from the Royal Mile
Stirling - visit the Castle & William Wallace monument, great landscape.
Drive through Trossachs & Lowlands,
Climb/Walk the Ben Nevis
Visit Ben Nevis Distillery
Drive through Highlands Lochs - Lochy, Duich, Ness, Towns - Glenshiel, Dornie, Castles - Eilean Donan Castle (Highlander, 1986), Uhquart Castle
Arrive in Portree & Isle of Skye
Drive through Isle of Skye
(camping highly recommended)
Drive to Inverness, flight to Dublin
Temple Bar in Dublin
Escape for your last day to Connemara (west) or Macgillycuddy's Reeks (south)
Flight from nearest airport
Fabien about 4 years ago