I don't have a definitive answer, but perhaps I can get the conversation rolling. Jeff Quinn of Gunblast Magazine compared the size of the New Vaquero cylinder and frame with that of similar revolvers. He did not include the Super Blackhawk, but he did include the Old Model .357 Mag Blackhawk and the Old Model Vaquero. Dimensions here are listed in inches:
THREE GUN MODELS: --- Old Vaquero ----- New Vaquero ---- Old .357 Blackhawk
Cylinder Diameter --------- 1.732 -------------- 1.675 ------------- 1.672
Cylinder Length ----------- 1.703 -------------- 1.610 ------------- 1.602
Frame Window Hdight ----- 1.763 -------------- 1.700 ------------- 1.700
You can see that the New Vaquero cylinder appears to be at least as beefy as the Old Model Blackhawk. But the Old Vaquero's cylinder appears to be thicker, and its frame was more like that of the SBH, (if I'm not mistaken). Does that mean the New Vaquero is at least as strong as the Old Blackhawk but not as strong as the Old Vaquero? You decide. That brings up another other question: that of frame specs. (thickness and kind of metal used). The Quinn article does not give that information, and I have not taken time to find it.
I'm having enough fun with the standard pressure stuff, but I would also like to know how much is too much for this fine shootin' iron.