I think one of the reasons that temperatures vary so much is that many engines vary on the fin cooling areas. Older engines had less and the newer square engines have much more. This results in cooler temps for the newer engines. Most modern engines can be converted to gas without overheating, despite running much hotter temps. Many gas engines have that hot metal smell as a normal course of their running, maybe not as much, but I have noticed it. So maybe the main damaging factor with running lean is not overheating, but lack of lubrication.