If you look back at the older Speer loading manuals, numbers 6, 7,& 8, they show higher velocity loads for the 45 Auto Rim, that they do for the 44 Special, or the 45 Colt.
Their top load for the 45 AR is 15 gr of 2400 with a 240 Cast SWC for 1155fps or 1192fps depending on which manual.
They also show a top velocity with a 200gr jacketed bullet of 1345fps with 14gr of SR4756.
They get 1330fps with 11.5gr of Unique.
Those loads are listed as Max and were fired in a 6 1/2" S&W Mod 1955 Target, not a test barrel.