I've got best accuracy with medium burners, 4895, 4064 and other powders in that range.  4350 does well too.  I've played with a lot of different slow burners, but when I get up over 40grs with them, the accuracy isn't there anymore.  I'm loading 168 and 190BTHPs, so there's a jump to the rifling.  My Garand doesn't care about that jump, why should my Krag?  Actually, if you keep rounds below magazine length, even the 220RN has considerable jump.