Let me preface by saying, I don't have any rechambered Handis. That said, I think it might be most prudent to just use a max of Ruger loads in .45 Colt, if one determined it was absolutely necessary to need that much. Personally, I would use my .45-70 if I needed more than what standard .45 Colt would deliver.
One of the sihlouette techniques is to trim brass so it's exactly the length of the chamber. That eliminates mismatches in chamber length and allows the cartridge to be custom fit to the chamber. A .454 Casull could be trimmed until it fits the chamber, which may help maximize the accuracy potential.