I've always understoood that you want to keep weight out of the ends of the boat for the reasons Ed stated, and also to prevent "hobby-horsing."
There is only so much you can do to get excess weight out of the stern.
You're stuck with the outboard engine you've got, even if its heavy.
I've drilled holes in the keel void at the stern looking for trapped water, but only found a few ounces.
I've also cut open the floor of the motor well and scraped out the wet styrofoam. The styrofoam, even wet, was very light. The area under the floor is not very big either.
If you're obsessed with this issue you could try these options first. (But only because water trapped in the boat is detrimental for other reasons).
At least on the Commander, the only place to put weight forward of the mast is in the forepeak or the water tank. I've opted to keep the water tank at least half full because I think the boat was designed to ride that way. She seems to sit on her lines.
Frankly, I don't think 60, 80 or 100 lbs up front is going to help or hurt matters too much one way or the other. Still, I would hesitate to put any more weight in the boat at the ends.
The problem of excess beer weight is easily solved.