I have the 4.5 XDm in .45 ACP and I love it, Thumper has it right, the heavier recoil spring will help counteract the heavier load and it will accelerate the slide back into battery. The suggestion for heavier mag springs for .45 Super was also spot-on. Having said that, I shoot a steady diet of 230 gr. JHPs loaded to 900 FPS that are very accurate and that I can shoot rapidly with accuracy. Before you get too far engaged into the .45 Super, I'd recommend trying it out with .45 +P. I'll go one step better because you can get +P velocity without +P pressure by loading your .45 ACP rounds with Ramshot Silhouette. If you dig back far enough you'll even find data for Enforcer that will give you .45 Super like velocity at standard .45 ACP pressure but using a large magnum pistol primer. +P with Enforcer almost makes the need for Super moot. You'll need to go back to the Ramshot reloading guide's #1 and #2, maybe #3 but don't hold me to that. Nothing wrong with .45 Super IMO but I just can't find anything I'd need to shhot that I couldn't do with a good handload using Ramshot Silhouette or for a more powerful load, Ramshot Enforcer. That includes pigs here that easily get to over 300 Lbs. with some getting close to 500 Lbs. That's the toughest test in these parts.