OK, have solved problem!
BIOS will NOT recognise a HDD drive as UEFI bootable UNLESS "fsX:\EFI\BOOT\BOOTX64.EFI" exists.
Copied fsX:\EFI\ubuntu\grubx64.efi to fsX:\EFI\BOOT\BOOTX64.EFI, and system is working.
Missing GRUB menu is actually expected behavior, according to what I've found. Once you have a successful boot in Mint 16, GRUB sets itself to not show the menu until a boot fails.
Have also needed to add a "rootdelay=10" to accommodate my SSD booting inconsistently with "root device doesn't exist" type of error.
Now, to fix the machine restarts instead of powering off when Linux "shutdown" command is issued. One post said this would be fixed by disabling Wake On LAN, but that didn't solve it for me. And also to fix the Windows 7 freeze, if I can.