I observed that the boot path saved even with power cycle or reload without Save.
In other words, the boot variable is automatically saved somewhere, maybe not in startup-config.
I'm talking about the BOOT path-list in "sh boot":
Switch#sh boot
BOOT path-list: flash:c3550-i9q3l2-mz.121-22.EA8a/c3550-i9q3l2-mz.121-22.EA8a.bin
Config file: flash:/config.text
Private Config file: flash:/private-config.text
Enable Break: no
Manual Boot: no
HELPER path-list:
NVRAM/Config file
buffer size: 393216
Changing the boot path with "boot system" and pulling the power cord, or reloading without saving, the switch comes up with the new path.
Playing around today with 3750G and 3550.