In 1985 I purchase a very expensive (at the time) 60 lb at 28 (marked and scaled) "custom bow" to go on my first elk hunt. I got it tuned up with 2117 al arrows with zwicky eskimo heads that weighed about 540 grns. At the time, everyone told me it was a great elk setup. It chronographed at 169 -171 fps with that setup. This was before fast flight strings were common.
Today, I shoot a Bear takedown with fast flight that is marked 45 but scales (same scale) 47 at 28. It shoots an axis shaft set up with a Zwickey, single bevel no mercy head and heavy adapter that weighs about 545 grns. It chronographs at 167 fps.
So the two bows produce very similar momentums. There is a lot more to it than just bow weight.
The Bear bow has some advantages over the heavier bow. Primarily, I draw the lighter bow about an inch further and shoot it much more accurately than the heavier bow. It uses a fast flight string and that helps. Not to mention that the skinny, weight forward arrow should provide better penetration. I have not killed as much game with the Bear (I've only had it 3 years) as the original bow, but I have killed enough to feel the combination gives as good as or better penetration (I haven't hunted elk with it yet though, maybe this year).
If you are concerned, spend some time on Tuffheads website looking at the linked articles linking momentum to the size of game hunted. Use their momentum calculator and you can probably come up with a combination that will make you comfortable.