My girlfriend and I completed most of the itinerary you have in about 5 days. Granted the pace was pretty challenging, we managed to see what we wanted to.
We left Orlando at about 7pm (after a full days work) and got into Glasgow at about 8am (both times are estimates, cant remember exact times), rented a car, stopped for a bit at Loch Lomond then headed straight to Ft. William (we were running on adrenaline, so a full day in Glasgow would be good for you to catch your breath) where we proceeded to hike to Steall Falls. I don't think I've ever been so exhausted but it was absolutely worth it.
Day 2 we left Ft. William, toured to Eilean Donan, drove over the Skye bridge and took a boat tour of Kyleakin (which was awesome--seals, salmon fisheries, mountains, and WWII history), then drove from there to Urquahart Castle and Loch Ness and finally settled in Aviemore (recommend booking ahead of time, the town is small).
Day 3 we left Aviemore, toured two distilleries in Speyside then drove down to Dunnotar Castle (one of our favorite castles in Scotland). From there we drove to St. Andrews and toured the course and town for about an hour then made it to Edinburgh by like 9:30pm
Day 4. Hop-on-hop-off tour of Edinburgh--got out to tour Edinburgh Castle and walk up Calton Hill, drove to Haddington to see my great-great grandmothers grave at St. Mary's church, and back to Edinburgh for a drink at a few different pubs.
Day 5. Drove to Berwick-Upon-Tweed (like an hour or so from Edinburgh), spent a few hours visiting the ramparts and town. Drove to Dunbar (which is a really cool city) and then back to Edinburgh and finished the day with a sunset hike up Arthur's seat--then an absolutely phenomenal steak dinner at 'Steak' in Edinburgh--the Aberdeen Angus was awesome :)
Day 6. We rented the car in Glasgow, so on the way back for our 5pm flight, we stopped by Stirling and saw the castle and Wallace Monument, and toured around Glasgow and saw a few of the soccer complexes.
We did a ton at a pretty intense pace but covered everything we wanted to!