I've got a .54 Plains Pistol such as yourself.
I believe I've clocked a 225 grain ball going over 1100 fps using 50 grains of Swiss 3f. I may have to repeat that again since it was years ago. I do remember being astonished at the velocity reading on my chronograph.
Sam Fadala's Muzzleloader Loading Manual lists a velocity over 900 fps with 40 grains of Goex 3F. For whatever reason, Sam did not attempt the 50 grain 3F maximum charge.
So I would imagine that 50 grains of 3F would put you comfortably in the 1,000 fps mark no matter what powder or conditions. And considering a 225 grain ball at those velocities - yes I would say that is definitely deer medicine at the distance you mention.