Just to top and tail this thread for future readers, Glen Artney-Callander is perfectly fine for a cx bike despite recent heavy rain, although a mtb is naturally faster on the purely off-road section.
The Glen Finglas loop from Wild Trails vol.1 is great on a cx bike, the only issue being that one is obliged by the continuous steep ramps to repeatedly beast it to the extent that you don’t get the opportunity to enjoy the scenery. The brief and rare glimpses were stunning, but no opportunity to cruise.
I had planned to go up Glen Ample but teh multitude of highland cows and calfs made me think the better of it so I took a detour up Loch Lubnaig.