Thanks for the good suggestions.
I had to leave for the weekend and left the computer on while I was gone.
When I returned, the system had booted and was working fine!
At this point, it looks like two things were going on...
1. The EZ Overclocking somehow was unstable and crashed the system.
2. Rebooting should have worked to reset back to default settings, but an external USB backup HDD was plugged in and the BIOS was waiting to boot on that for a LONG time before it gave up and booted the SSD.
So things are working fine now, and I'll be happy just to run my 8700K at default settings, which is fast enough...