When is an OK time to ride the scottish highlands?

My wife and I have been inspired by the youtube videos of riding in the scottish highlands, particularly Fort William and Top Chief. My wife turns 40 next year so we're trying to plan a special trip where we can get a couple days riding in alongside experiencing some of the country. The internets tell me that the rainiest months are August thru October, and we were hoping to go late summer early fall. Is there a "best" time ride the area? Does it matter?