Once you understand all the factors involved in actually building solid lean mass you will begin to answer your question.
In reality, for real actual lean tissue gained, maybe 2-4 lbs. This is taking water, fat, blood volume out of the equation. 2-4 lbs of solid lean muscle mass!!! Plain and simple. Again, many factors rely on this result. Type of compounds used, diet, training, water intake, cardio etc. Then of course we have the ever present......Genetic ability to build lean mass. Yes all of these are either limiting or gaining factors, But 2-4lbs would be a reasonable estimate.