I would argue that if you want to shoot 400 grain bullets you should move up in diameter. A 400 grain .452 bullet is very long, eating precious case capacity. I have experimented with really heavy-for-caliber bullets in a number of calibers to include 400 grain bullets in the .454 (while they worked fine, they didn't do anything the 360 or even lighter loads did), 405 grain bullets in .429 Magnum, and even 700 grain bullets in .500 S&W. They didn't work particularly well as they wouldn't stabilize in flight or in the test medium. When bullets go sideways, they don't penetrate worth a darn. If you want a good backup load that is mild, you can load your .45 with 300 - 335 grain bullets at low velocities and they will penetrate like there is no tomorrow. None of the heavy bullet loads we tested were able to achieve much velocity (no case capacity), so within the limited confines of our revolver cartridges, I believe you will be much better served with a lighter bullet. JMHO.

Stock Ruger .45 Colts have a 1:16 twist while the customs will typically be fitted with a 1:18 twist barrel. I don't think there is enough of a difference to affect the way they shoot though there are those who will argue it is enough of a difference.

Also interesting to note that John Linebaugh, in the early days, would fit custom .45 Colts with slower twist barrels to make them more shootable with heavy bullet loads. Shootable how? A fast twist can make the gun torque and subsequently twist in your hand when running them hard. The slower twist made them more "gentle."