Great ride report my friend, makes me very ashamed that I have a place in Donegal that all my family come from and was born and live here in Scotland and at the age of 49 have still yet to tour both. It was only recently on one of my many trips over to Ireland that I decided to make a detour from Larne around the Antrim coast to Derry, then onto Donegal. It was a fantastic day and we enjoyed the Carrick-a-rede rope bridge and the Giants Causeway. I will explore the North in greater detail sometime soon.
As for Donegal, most riders tend to visit Letterkenny or Donegal town and miss the real Donegal which to me is the Rosses area, Bloody Foreland and the west coast, next trip you should visit Glenveagh National Park, you could also set a day free to climb Errigal mountain, Donegal's highest mountain.
Sligo, Mayo and Galway I visited back in the eighties and the Conemara coast is as stunning as Donegal.
Your RR has now inspired me to concentrate on a tour of Ireland and Scotland as both are on my doorstep instead of Europe next year. Look forward to the rest of your report.