Back in the day, I reconfigured my late unlamented Colt 1991A1 to 45 Super using information and load data from this site
http://www.realguns.com/. you'll have to roam around through the archives to get the details.
I used a then experimental Wolff 28lb recoil spring to get a 225gr cast bullet to a chrono'd 1150 fps. Powder was Alliant Power Pistol. The load didn't seem to bash the frame or damage the gun. It was hard to hang onto, and as a result not as accurate as a +P 45 ACP load. Later on, I downloaded the 45 Super cases to get around 1000 fps and the loads were much more useful and accurate.
I wouldn't try it again on a standard 1911. I might go to 900 or 950fps. If I needed any more horsepower in a 1911 frame I would go to a 460 Rowland.
This is my opinion, your opinion may vary.
ZM