Hmmm, not sure where to start, since there are so many variables involved. Thinner arrows, heavier broadheads, etc...etc...
Basically an arrow is bringing an animal down by making huge slices and causing a bleed out. If you already have good penetration with a 100 grain head, adjusting to a heavier head won't make that much difference. Again we are not talking impact energy as we would with a bullet, since they are two different killing modes. Now, a bump up in draw weight can give a boost in speed, even with a heavier head, and if your looking for a change in penetration power this would probably be the best change you could make. This would help if you contact bone, but remember that even a bullet can be deflected by bone or even a twig between you and your target.
Changing the spine stiffness of your arrow can affect speed as well by reducing arrow flex and translating more of the release power to the arrow. So, having said all that I would experiment with some stiffer arrows and adjusting the draw weight before I moved up my broadhead grains. Remember that all of these are going to change the performance of your shots and the accuracy you may have started with, so take some good notes as you progress through the alteration of your arrows and weights. You may find you want to go back to your original starting point and this will help you keep that, plus give you a good record of what you liked and didn't like.
Hope this helped some.