I don't think pre-1895 Colt Peacemakers were ever made in either caliber, just .45 Colt??
Colt chambered the Single Action Army for 44-40 in 1878. 44-40 was the second most popular chambering of the SAA, only surpassed by 45 Colt.
The total number of 1st Gen Single Action Army revolvers chambered for 45 Colt was 158,885 in the four variations, Standard SAA, SAA Target, Bisley, and Bisley Target of the SAA.
44-40 was the second most popular chambering, with a total in all four variations of 71,391. The 44-40 version of the Colt Single Action Army was the only version of the SAA that had its own 'model name', the 44-40 Colts were known as Frontier Six Shooters, as can be seen in this photo of an antique 44-40 Frontier Six Shooter.
The third most popular chambering of the SAA was 38-40, first offered in 1884, with a total of 50,520 SAA revolvers chambered for that caliber.
The next most common chambering for the SAA was 32-20, also introduced in 1884, with a total of 43,264 in all four variations.
I am not going to go through all the chamberings of the Colt Single Action Army, but the 1st Gens were eventually chambered for a total of 30 different cartridges, the great majority of them being offered before 1900. Only two chamberings were first offered during the Twentieth Century:38 Special in 1930 and 357 Magnum in 1935.
So clearly, if a Cowboy was able to afford a revolver and rifle chambered for the same cartridge, the most common combination would have been a Colt Frontier Six Shooter and a WInchester Model 1873, both chambered for 44-40.
Let's not kid ourselves here, the idea of a cowboy owning this pair of firearms is largely myth. The price of a new Winchester Model 1873 in 1873 was $38 for a simple Carbine, up to $60 for the fanciest grade of 1873 Rifle. The cost of a new Colt in 1873 was usually around $12. Most Cowboys only made about $20/month if they were lucky. Very few would have been able to afford these prices. Much more common would have been Cap & Ball revolvers surplussed out of the Army, such as the Colt 1860 Army or 1851 Navy, or 1858 Remington. These were commonly available for around $5 at the time.
There was a gun ad in the 1990's. I can't remember which one, maybe Marlin. It was for a lever rifle to be a companion to a 6-shooter like a Colt Peacemaker or a Remington in .45 Colt. Back then it instilled in my head the notion that there were both pistols and rifles even back in the Old West that could fire the .45 Colt. Now, people are saying here that .45 Colt rifles did not exist during pre-1895 Old West times. The ad romanticized the Old West cowboys who wanted both a handgun and a rifle that could conveniently fire the same ammo. Now, I'm finding out there were other companion combos in the Old West which could fire cartridges other than .45 Colt. When it comes to original cowboy guns, I'm fascinated by the whole COMPANION concept. I'm sure there a lot of reproductions that could give one such a companion pair of guns.
Whatever you remember from that advertisement, I am here to tell you no rifles were ever chambered for 45 Colt during the 1800s.
NONE! Take a look again at the photo of the old 45 Colt cartridges I posted earlier. The rims were simply too small to be effectively grabbed by the extractor of a rifle. Not a problem with the old SAA revolvers that poked the cartridges out from the inside, but a rifle extractor would simply not have been able to grab those tiny rims. As I said earlier, it was not until sometime in the 1980s that rifles were ever chambered for 45 Colt. The old Winchester cartridges, such as 44-40, 38-40, 32-20, and 25-20 were designed specifically to be rifle cartridges. They had larger rims, which could be effectively grabbed by the extractor of a rifle. It was easy for Colt to chamber these cartridges in the SAA, because their overall length was not too great to fit into the cylinder of the SAA, and there was enough room between chambers to accommodate the larger rims.
So, it seems like the Winchester 1973 and the Remington 1875 in .44-40 would have been the two original cowboy companion guns. Something cowboys might have carried on the first cattle drives since the advent of the cartridge. Somebody else here might want to cite another pair of Old West cowboy companions. A SA revolver and a lever rifle of the Old West sharing a common cartridge.
I hate to keep poking holes in your assumptions (actually I am having a good time doing it), but the Remington Model 1875 chambered for 44-40 was an exceptionally poor shooter. They tended to be very inaccurate because the chamber throats had been cut too large for the 44-40 bullets. Take a look at this pair of targets fired from a rest at only 15 feet. Trust me, I am not that bad a shot, my Remington was spraying bullets all over the place because of the oversized chamber throats. I don't recall right now exactly how big the chamber throats were, but they were much too large for a .428 diameter bullet. The Remington Model 1875 was only chambered for 44-40 and a proprietary Remington cartridge called 44 Remington. There were a very few, probably less than 2 or 3 that were chambered for 45 Colt for Army trials. The 44 Remington cartridge had a large heeled bullet that was larger in diameter than a 44-40 bullet. The speculation among collectors is that chambering the 1875 Remington for 44-40 was a bit of an afterthought, and cylinders were remachined for 44-40, with chamber throats that were much too big. Anyway, I was grateful all my bullets went through the paper pointy end first, and none of them went through sideways.
The Army rejected the Remington Model 1875 for several reasons. Chief among them was the fact that the ejector mechanism of the Remington was exposed to the elements.
The ejector mechanism of a Colt was protected from the elements by the ejector housing.
The bottom line is, the 1875 Remington was never as popular as the Colt Single Action Army. Colt won their first Army contracts in 1873. The army rejected the Remington in 1875. Colt already had such a strong foot hold in the revolver market, both Military and Civilian that eventually there were 356,581 1st Generation Colt Single Action Army revolvers produced, only about 25,000 Remington Model 1875 revolvers were ever produced.