I did some poking around and may have answered one of my questions (bach thrust of 44 mag vs. 45 colt +P). Using a back thrust calculator, I came up with a back thrust of 5,426 pounds for the 45 Colt (using a case diameter of .480 and a pressure of 30,000 psi) and a thrust of 5,902 pounds for the 44 mag (case diameter of .457 and a pressure of 36,000 psi). It would appear that the 45 Colt +P rounds have significantly less back thrust than full power SAAMI 44 mag loads.
For those interested, Reeds 45 Colt +P ammo is rated at 21,000 psi (per an e-mail response). Using the on-line formula I found, the Reeds ammo 45 Colt +P rounds have a back thrust of 3,798 pounds while the full power 44 mag rounds have a back thrust of 5,902 pounds. The full power 44 magnum load has about 55% more back thrust than the Reeds 45+P LC.