Howdy
A couple of things.
Not too sure why you are limiting yourself to 7 1/2" in the model P and 4 3/4" in the Open Top. There are more barrel lengths available, you can get either model with a 4 3/4", 5 1/2", or 7 1/2" barrel.
The Rollin White patent, which Smith and Wesson controlled, regulated who was legally able to build a cartridge revolver with bored through chambers. It expired in 1869. Colt had been sitting on their hands and did not have a new design of a cartridge revolver ready to produce when the White patent expired. It was 1873 before they released the Single Action Army (Model P) with its stronger top strap frame. Instead they came up with several different 'metallic cartridge conversion' designs that basically modified their existing percussion pattern cylinders.
The model marketed today as the 'Open Top' is probably the best or these designs. Rather than relying on the narrow V groove on the hammer of the percussion models for a rear sight, the Open Top has a rear sight attached to the rear of the barrel. This makes them a bit easier to sight.
Even so, these are still a compromise design. They are not as strong as the SAA with its top strap design, the barrels on the Open Tops are fastened to the frame just like any Colt pattern C&B revolver by means of a wedge running through the cylinder arbor. And frankly, I am surprised they are chambering them for 45 Schofield and 45 Colt. The SAA cylinder is larger in diameter than the old 1851 Navy and 1860 Army models the Open Tops are based on. Unless the 45 Open Tops have a larger diameter cylinder, I would be leery of shooting them very much with full power loads. There simply is not as much metal there. Yeah, I'm sure they have been proofed, but still.......
Also, be aware that the model Cimarron is marketing as their 1872 Open Top Army has the larger 1860 Army grip frame, their 1872 Open Top Navy has the smaller 1851 Navy grip frame, the same grip frame that was eventually used in the Single Action Army. A little bit smaller if that matters.
The Open Tops are very cool and very distinctive looking guns, and if that is what appeals to you, go for it. I can tell you there are not very many of them that show up at Cowboy Action Shooting matches, the vast majority of pistols are either Rugers or variations of the Single Action Army. The Open Tops are very cool to look at, but most choose a Top Strap design for competition.
