MN is right although I wouldn't have been that blunt. If your arrow spine is heavy enough to handle the 125 grain broadheads and the fly true for you there is no reason to switch. A 100 gr BH will probably only give you about 5 fps more speed (if that). But it will definately give you more penetration. Which is a plus for elk.
As for the Muzzy 125s I also used them for years but today there are better heads out there. One of the best flxed blades are the Slick Trick line of broadheads. Muzzy Phantoms are also a good choice.
The mechanicals today are better than the earlier ones being more reliable. But nothing, and I mean nothing beats a good flying fixed blade.