Juggling lenses in the Islands is tricky, and adding a long prime makes it even more difficult, as you NEED a long and short zoom as well, almost at all times.
I brought both my 500mm f/4L IS and my 100-400mm.
Two bodies is a must, if you want a long lens on. Even 100mm gets too long, but at the same time, 500mm was often just right! (I even used a 2x on one occasion!)
If you can fit it Ian, I'd take the 500mm and that Sigma 100-300mm, then the 17-50mm and 10-22.
If you don't want to lug the 500mm around, then it's your 400mm f/5.6 for the long work.
To the OP, take your 100-400mm for sure. Be ready to switch to something under 100mm, preferably already on a second body.