I will not go into working up a load for your gun, but, H or IMR 4227 works great in mine when I use Winchester WLP primers, when I "reached" the most accurate-and safe loading in my 12" .44mag there was minimal unburned powder left. Those powders are very uniform but they require to be worked up to achieve that uniformity, meaning that they work best at or near a max load. In .45colt I would use a faster powder as the case is not as thick in the web area as the "magnum" case is. AA#5 and Unique are great and should provide all the power you would ever need in a single shot. If you want a little more velocity AA#9 is great as you don't need to stuff a compressed load in the case to get uniformity like the extruded 4227's.
You can easilly get the same velocity with CCI300 primers and AA#5 in your closed breech, as AA#9 and magnum primers would do in a 7.5" revolver, with the same bullet of course.