RE: Powder to powder?
Other then Black Mag3, I've been lucky enough to test a number of different powders including; Goex 2f & 3f, Triple Se7en 2f, Pyrodex Select, Pyrodex RS, Pyrodex P, Clean Shot, Pinnacle, and Swiss 2f & 3f powder. All of them will give good accuracy with sabot projectiles for the most part. What you need to consider is the conditions you shoot and hunt in. If it humid, dry, snow, etc? This might be more of a factor on your powder selection.
Next consider how much you like to clean your rifle. Is fowling a problem for you? Some powders you need to swab a lot more then with other powders. Also clean up depending on the kind of powder will vary, but remember... you still have to clean them.
I personally shoot a lot of Goex 3f in my inline rifles. I also like Triple Se7en. This last winter I tested some Goex Pinnacle and it shot excellent with light weight sabots. It did not shoot so well with heavy conicals...