Agree there's more than enough to see round that area. Other option is if you are heading down the Kintyre peninsula, you have a choice as to which side to launch as well - lots of places to see on the Clyde side as well, and gives you options if the wind gets up to go for a relatively sheltered cruise (selling point to persuade those who must be obeyed
) - just bear in mind at the bottom end of Bute it can get quite lumpy at the worng state of the tide on a windy day.
If you don't get permission to "go to sea", one to watch is Loch Earn. They'll allow you to launch & use a "speedboat", but be prepared for a sharp intake of breath - as it's a conservation area (or somethig like that) launch / recover fees for anything up to 50Hp - £10. Above 50Hp - £25!!!!
Which wouldn't be so bad if you had a lot of water to play with, but even at a leisurly 16 Knots it only took 15 mins to do the whole length of it! If you have a sib with a "small" engine it's quite good - launch at the Lochearnhead end, potter down to Fallin, and there's a hotel by the water does a good bar lunch.