I am partial to the .58 and that's why i own 2 a 1:70 and a 1:48 twist. Both are Hawken styled rifles. Honestly I don't put to much thought of ballistics in muzzleloading. It seems to me that a heavy projectile is what gets the job done. Being that drawing a ME moose tag is a once in a lifetime opportunity; I would go with the rifle that is most comfortable and accurate and place your shot. I believe both the .54 and the .58 are adequate enough to tackle the job. Moose are not all that difficult to kill.