I have been playing with this issue for the past few months and several bows. The question for me was where is the line between extra lams giving you more smoothness but additional glue lines detracting from performance. I build primarily light bows. I've now done 4 lams up to 55# and 2 lams down to 22#, plus a one lam 30#. All of these are 66" and 68" longbows. (The only bow worth building, of course 8^)
My conclusion, for whatever it might be worth, is that for my bows of roughly 30# and under, I'll stick with two lams, 35 to 45# three lams, and above 45 I'll go to four lams. If I were to build higher weights, like 55 to 60 and up, I'd definitely be tempted to go to five, but would not go over that. Fortunately, I have no interest in bows that heavy.