The rate of your gains depends on many things. The main things are staying strict with your diet and maintaining a good routine for your experience level.

Stay fairly strict on a high protein diet and kept up your training. Also keeping your alcohol intake to a minimum helps wonders... ask me how I know... I would say you could gain the 25lb of muscle in ~2 years. Oh yeah, good solid sleep makes a huge difference as well.

It depends on your genetics (and *alot* of other things) to a certain degree as well.

IW