As I modded Fallout 3 more and more, getting XP from kills was quite easy as there were many things to kill.  Well Rested was meaningless as I only slept to heal up.
This is why I went and changed it from boosting the player character's experience gain to boosting the player character's damage output.
Its only a measly 20% so you won't become a demigod.  Might edge it lower if it turns out to be unbalanced.
If you do want to tweak this boost, fire up geck, load up this mod, find the well rested ---->PERK! <----- and adjust how much that the damage output is modified.  Make sure it is greater than 1 or you will do less damage if you are well rested.

update 1
Forgot how to properly save my work, now saved as .esp and uploaded in a working model.