if you want really simple #'s to compare just multiply the speed X grains.
Gives the same % difference just don't have to remember 225218...lol
675*160=108000
580*173=100340
500*181=90500
if...
108000=100% (108000/108000)then...
100340=about 93% (100340/108000) and..
90500= about 84% (90500/108000)
What does all this mean...who knows..
One has the most energy, one has the least.
Every one will kill.
If you can shoot it well at all hunting distances I'd go with the heaviest/most energy.
What's fun is to keep adding wt till the wt*fps drops. Then see what you think when you back back down a few grains to the most "energetic" arrow.
Have fun
Good luck on the elk!!!!!