RE: .44 magnum rifle
My sister hunts with one. Ballistically, the .44 Mag from a rifle is good medicine for deer out to 100 yards. You said it's a good shooter out to 50 yards. I'd say if you can consistantly hit a pie plate out to 100 yards, don't be afraid to use it on a deer up to that distance. Good luck!!
EDIT: The italics part... I'm talking about numbers I've seen in the Shooter's Handbook. Most ammunition maintains over 1000 lbs of energy and decent trajectory out to 100 yards. I would guess there are some loads that do not.