Wow, I believe the whole root of the problem has been discovered, thanks to one of the points on that checklist. I looked at the Event Viewer under the Admin Tools section and found over 2000 alerts, all occurring within the recent time frame of increased boot time.
Here is a sample of some of the most recurring:
= The following boot-start or system-start driver
(s) failed to load:
= Event filter with query "SELECT * FROM __InstanceModificationEvent WITHIN 60 WHERE TargetInstance ISA "Win32_Processor" AND TargetInstance.LoadPercentage > 99" could not be reactivated in namespace "//./root/CIMV2" because of error 0x80041003. Events cannot be delivered through this filter until the problem is corrected.
=The driver detected a controller error on \Device\Ide\IdePort1.
Explanations as to what is happening, much appreciated.