In a .458 cal. rifle built for smokeless powder, you can shoot H 4198, VV N-120 or Reloader #7 without 4227 to help in ignition. I have never used a duplex load that I could get the velocity I wanted without blowing the sabot.
I used to shoot 66 gr. of VV N-120 with the Barnes 195 gr. bullet W/Harvester sabot @3000 FPS.
I have used 73 gr. of Reloader #7 with the Barnes and 72 gr. with the Pittman 225 gr. Accumax bullet for 2675 FPS.
I have shot these powders in below freezing temps and never had a problem, but I always shoot Federal 209 primers or Federal 215 Magnum Match primers.
Just make sure the Barnes bullets/sabot are tight going down the bbl. You may have to knurl them up a 0.001" or so. The Pittman is a little bigger at .402
I always keep a log of my shooting and loads.
Good luck and have fun.