New bios version 1.11.3  (Nov 12th 2021), has solved the issue.  Problem solved.
My new (unused) 7420.  Turned it on, let the Dell command update do its thing.   That included bios 1.96  and numerous Intel patches. Now the cold boot takes 58 seconds to show the POST screen logo.     It looks to be doing the thorough boot check from cold every time.  The BIOS is set to minimal fast boot.   Clearly a mistake somewhere causing it to do this long boot check on cold boot.  How to fix?
7420 : 1 minute cold boot, after bios v1.96