Gourock-Dunoon ferry, ride north for a couple of flat miles, turn west onto a fantastic road, steady long climb for a while, long descent, very steep climb (think start of Lecht steepness), then descend onto a fairly flat road with one steady climb, descent to Colintraive for the world's most over-provisioned ferry service to Rhubadach on Bute, then largely flat road towards Rothesay. No food stops until very near the end on Bute so food probably needs to be carried.
Also, parking is a faff as getting between Wemyss Bay and Gourock involves riding along a crap, busy main road.