I can't say what the CAA might make of granting you an unrestricted Class 1, knowing you have a 7mm stone, but if it helps, I have very recently had my gall bladder removed by laproscopy (keyhole surgery). After several bouts of severe abdominal pain (2 episodes in flight), I had an MRI scan which showed 3 stones, the largest was 9mm. The opinion of my consultant and the surgeon, was that removal was the best option. Recovery was quick - just a few days of feeling lethargic (the Olympics were on TV!) and some localised bruising. No restrictions on diet and I feel that if I was to reapply for a Class 1, the CAA would probably be agreeable, with a report from my own Doctor.
PM me for further if you want.