Well, I am very far from being a metallurgists of any kind, but since it was I that introduced the topic in another thread, I'll reply to the best of my knowledge:
The data I was referring to in the other post came from one of James Kelly's articles in the Buckskin Report, which Dan Phariss scanned and from whose photobucket I stole it some time back. It gives the Izod impact test results for bushelled (recycled scrap melted together) wrought iron as 58.5 ft-lbs, and 1137 as 47 ft-lbs. Unfortunately, the impact test values for cold-drawn 12L14 are from a different impact test - the Charpy test (14 ft-lbs longitudinal, <5 fts-lbs transverse) - and while according to the interwebz one can just multiply the Izod by 2.738223 to get the equivalent Charpy figure, I'm pretty skeptical that it is that simple....particularly since there is more than one kind of Charpy test! I did go look at a couple graphs comparing Izod to Charpy based on testing done in the mid-20th century, and while it differs depending on the type of notch used in the test, it does look like an equivalent Izod on that sample of 12L14 could not possibly be higher than the low 40s (assuming V-notch Charpy test and a result well over to one side of the bell curve) and is much more likely to be around 20 ft-lbs.
Again, there are some pretty severe limitations on that data, and I think that the 1137 and 12l14 used for gun barrels is likely stronger than the samples tested (1137MOD because it is specially formulated for gunbarrels, the 12L14 because is stress-relieved instead of being merely cold-drawn). However, it sure looks to me like the assumption that any modern steel is automatically superior to the the old wrought iron is rather questionable.
As for the relative strength of 1137MOD and 12L14 - even run of the mill 1137 has only one-half to one third of of the sulfur content, no added phosphorous beyond the max allowed under AISI specs (.04% or less, versus .04-.09 for 12L14), and no lead whatsoever, and this stuff is specially smelted, heat treated, and inspected with gun barrels in mind. We can (and have!) argued till our faces are blue over whether 12L14 is strong enough to be safe, but I don't think that anyone could seriously argue that 1137MOD isn't strongER than 12L14. If you want professional metallurgists opinions - the fact that one is rated is being produced for gun barrels and one is not is a pretty definitive opinion.