Just another 'total' stranger here ... but I load 20g of IMR 4227 under both 250g RNFP and 255g SWC in .45 Colt. Use a CCI-350 Magnum primer. One of the most accurate loads I've found. Taffin also liked this load. Only reason I don't load it often is it is a bit expensive to use for general use. Doesn't take long to go thru 350 cartriages (per pound)! Load it for my medium frames as well as for my large frame .45s.
As for modern .45 Colt SAA and USFA, Brian Pearce puts them right along side Ruger's New Vaquero and the Flattops (medium frame). Ie. They all can handle the Tier 2 loads for .45 Colt. tier 2 is defined around 20,000psi. They can't handle Tier 3 (Ruger Only Loads at 30,000psi). Tier 1 is SAMMI (14,000psi).
Brian Pearce .45 Colt PDF
Note that since the advent of the .45 ACP in the New Vaquero and medium frame Flattops, the Tier 2 mentioned above has been revised upward to around 23,000psi...