I did 40mgs for 10 weeks gained about 6-8 pounds when all said and done but dropped about 2%BF and hardened up ALOT. It is all in your diet but I would not go below 40mgs IMO.
My training partner always does 25mg cycles in the summer, just to maintain muscle while losing bodyfat. Works well for him...He's fuckin ripped and hard. His diet is flawless though, so I'm sure thats most of it.. He increases cardio a lot, and doesn't lose muscle, so i think the var at the dose works