Did you happen to notice that the photo you are referring to was posted by me back in 2007?
The only reason I showed the New Vaquero 357 Mag cylinder on the left is because I don't have a New Vaquero chambered for 45 Colt.
For a true comparison, the cylinder in the center is from one of the 'original model' Vaqueros with the large frame. The cylinder on the right is from a 2nd Gen Colt, you can see the Colt insignia on the rear of the cylinder.
Compare how much steel there is between the chambers of the large frame Vaquero cylinder and the Colt cylinder. That will give you a good idea of the relative strengths. A Pietta chambered for 45 Colt will be very similar to the Colt.
Here is another photo I have posted on numerous gun boards over the years.
Left to right, the cylinder from an Uberti Cattleman, Ruger 'original model' large frame Vaquero, and the 2nd Generation Colt cylinder. All three cylinders are chambered for 45 Colt, so it is an apples to apples to apples comparison. Clearly, there is more steel between chambers with the Ruger cylinder than either of the other two. I forget exactly how much, I haven't measured them in years. I seem to remember there is something like .050 of steel between chambers of the Colt and Uberti, something like .080 between chambers of the Ruger. I can measure them again if you would like.
A Pietta cylinder chambered for 45 colt will be very similar in dimensions. This is because the distance from the center of the cylinder to the center of the bore of the barrel is very similar in the Colt, the Uberti, and a Piettal. The Ruger cylinder is bigger because the distance from the center of the cylinder to the center of the bore is larger, so the individual chambers can be spread out slightly more.