No, I think you have got it about right.
I have fired maybe 100 standard steel shot cartridges, mostly 2.5" ones, and they feel just a shade hotter that the usual one ounce loads that I use in my Webley.

However I am sure that it is a bad idea to fire ANY steel loading through more than half choke, i.e. 0.020" of constriction. Others here have fired some of the Superior Steel loads and not enjoyed the experience. I am stocking up on Bismuth as and when...

HB