Dave,
The following is just my opinion.
I agree with not over-doing it. For N America 50-55 lbs will be plenty enough for anything here. Some will argue that "just enough" isn't ethical, because you may make a bad shot and leave an animal wounded. I see that point.
However, if you are a terrible shot with the heavy bow it is pointless.
For instance; If you don't hit the animal at all that pretty much ='s zero penetration. Furthermare, if you have excellent penetration, but it is on say the knee joint. Then you get a three legged animal that may or may not survive.
Shoot a bow that you are accurate/confident with and has a nice sharp broadhead at the tip of a heavy arrow.
You'll be in good shape.
Also think about the material a bow is made from;
A 70lb selfbow may shoot a given weight arrow at 150 FPS. Then, you get a modern recurve at 55 lbs with the same arrow and it too shoots 150FPS. Which was better the light or heavy bow?
-Charlie