Optimal? As much as you are accurate with. What is good one day may not be as good when you're stiff and tired, or wearing bulky clothes and don't quite reach full draw, or thwack an unseen twig, or, like I just did, shoot with wet puffs and fabric camo tape that robs a surprising amount of speed.
I don't ever recall thinking "Damn, I got too much penetration that time" or "Rats, I didn't use up all the available opening for a rainbow trajectory just then." I'd shoot a 100# bow if I could draw it 60 times in an afternoon of field shooting.
My two primary bows are 56# and 61# at my draw weight. I'm thinking they're about ideal for the areas I hunt. I shoot a 600 to 620 grain arrow. I have had several full pass-throughs with the 61# and the 56#er just stuck a Stos head 1-1/2" into a tree after passing through a whitetail's chest.