If you wanted to go totally overboard, how about doing a couple of days at the RSCs first, then down to Kilmartin via the Stirling area, allowing a quick break at the Castleton RA. Spend a couple of nights in Kilmartin, then (assuming timetables allow at this time of year) to avoid the roadly faffing of getting from Kilmartin to Glasgow, nip down to Claonaig and ferry to Arran swinging past Machrie and the lovely Stronach carvings, thence ferry to Adrossan, zooming into Glasgow in time to fly home?

I've been on that Kilmartin - Arran - Glasgow route in both directions (though I wasn't driving) and it was surprisingly quick. But I dunno how frequent the ferrys are when it's not summer.

You must fit Kilmartin in. It lives up to the hype.