Some great road cycling there. Roads are quiet, some challenging climbs, great scenery and also large sections of really good quality tarmac….there are a few gravel / haul roads but those might be a bit boring on a mountain bike, not much flow to them.
One of the best 25 mile loops in Scotland sounds close to where you will be staying- basically if you were to start Tighnabruich then head north up and over that climb, then take a left at the road end go along a mile or so and take another left over the C11 road (easy to miss the turn for this – i think the name of the climb is Bealach Maim) over that climb to Otter Ferry then head south over rolling roads.