I have quitr a few Ithacas with examples of both models. In my opinion the NID models rank as maybe the best designed, strongest and longest lived doubles produced in the US. When I shoot an Ithaca it is generally a NID model. The Flues and older models are beautiful guns, well made and a delight to handle but are generally not particularly robust guns. I own mostly higher grades in the older guns and don't shoot them a lot due to respect for their value and vintage. The NID's are generally capable (condition dictating) of modern loads. However, I still restrict all of them to light loads for the simple fact that I see no real reason for anything else.
RST factories if available are great. So were Polywads' offerings. For a 16,check out the 16 Gauge Societies spreadsheet of reduced loads for that gauge. It is perhaps the world's single largest source of low pressure 16 ga loads. I have never found it necessary to shoot a load over 6000 psi in a 16 gauge. I am even happier at 5000-5500.
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