I just made this using only three egg yolks, as instructed by the recipe on the bottle of key lime juice I picked up. I also used a reduced fat graham cracker crust. Still tasted great! Don't forget to save the egg whites for that classic meringue topping.
This is the recipe I use too- it is incredibly easy and knocks guests over! BUT, I totally recommend making a from- scratch graham cracker crust and serving with fresh whipped cream. Criminal!