I recently bought my first home, a 1940 Cape with single pipe steam heat. Two mains, each about 30' of 2" pipe. One main supplies 4 radiators on the first floor (two are double sized); Second main supplies 6 radiators including 2 on the second floor.

I understand the venting concepts. What I have a hard time understanding is how to quantify the capabilities of different valves...

Quantitatively speaking, for main vents, what is a Gorton #2 capable of accomplishing versus a Hoffman #75H? From what I have read I get the impression they sound comparable in application?

Also, for radiator vents... I'm even more confused as to how to shop for them? The tongue on the Hoffman 1A is a smart idea which I don't see on any other parts. I'm still confused quantitatively speaking as to what the capabilities are? I've read in forums where rules of thumb are noted ('use #x upstairs and #y downstairs)... but it doesn't seem that those numbers are industry standard? Why else would a #2 Gorton main vent be comparable to a Hoffman 75?

I am asking here because I grew up watching TOH on TV and explanations are always very thoughtful.