FIXED, I think.
Yeah, I'm not very clear.
On certain brands (not sure which at this point), if I try to force load from the last page in BIOS, it will flash to a few different BIOS pages quickly and then wind up on the last page again - in other words it didn't like it. But if I go to boot order and select the non-UEFI version of that brand, it works.
BIOS settings are:
Windows 8 Features "other OS"
Boot Mode selection "UEFI and Legacy"
Storage Boot Option Control "UEFI First"
Other PCI Device Rom Priority "UEFI OpROM"
I have no idea what if anything affects anything.
But I DO find that with F6 the boot order list is very much more touchy - it doesn't tend to remember the old stuff if I add a new one. I finally realized that and stuck about 5 brands in and booted to BIOS and added all the UEFI and non-UEFI version of them that it offered me. I still have to force boot on a couple of others. It now boots Linux USB flash drives fine.
Moral - use the same brand of USB flash drive!
Thanks to all of you for looking in!!!!!!