I believe only the 45 XTP's have the mag/non mag designations. When I started inlining I wanted to use 44 Mag - 454 Casull level loads. My velocities max at 1600 fps with both the 250 and 300 gr non mag .45's and recovered specimens look great.
A very nice thing to remember about muzzleloaders is that whatever game you hunt or velocity you desire , there is a bullet for you. For those of us who dont feel the need to pour 1/2 a can of powder down bore ( or cant afford to !) or are small statured , injured or hunt at modest ranges, a non mag XTP at 16-1700 fps is a dandy load.Hornady gives the non mag a very good low end expansion capability. This is useful as one of my max range criteria is based on the question of bullet expansion. In my experience , energy transfer is as important as the power of the load itself. I know that my 2 non mag loads ( 250 and 300 gr) are both way above their minimum expansion velocity at 200 yards ( 1006 and 1058 fps actual respectively) and the minimum for both is 800 fps. I believe , with its better low end expansion potential ( 800 fps nm vs 1100 fps mag) the non mag is probably the more versatile bullet.
Have to admit, won't see my rifle until tomorrow. It's sitting at the UPS Store now, LOL!
But... from all the charts I've been reading, etc. I'm not thinking I'll ever use more than 100 gr. of BP, Pyrodex of 777. (Bought some 777, so that'll be experiment #1.) So I'm with you, probably go with the 250 or 300 gr. XTP.
But to be honest, I'm eyeing some bullet molds too. I really don't want to be tied to sabots if I can get decent accuracy and energy without, and without serious leading.
If I can come up with ballistics similar to .45-70 or .50-90 I'll be happy (though probably not quite the same, probably won't use as heavy slugs). I'm planning to stick to a 100-150 yards as max. range, so no real drive to go to 150 gr. loads. I'm figuring, "if it looks like a tough shot with the fixed sights or the 4x scope, then don't take the shot". I've got pretty conservative estimates of my ability, which is probably the real limiting factor.
Anyway, just trying to get a handle on what I think my "standard" loading is going to be, hence all the thrashing of these issues.