impedence rule of thumb?

[Skeet Bonham]

i recently purchaced a crate gt412st cab and valveking 100w tube head. what would be the proper omhs settings for this set up? the cab has a switch for 16/4 omhs mono and an 8 omhs stereo. the head has 16/8/4 switch with 2 speaker jacks that can be paralleled. i looked through threads and online to no avail. if the cab is supposed to be at 8omhs do i have to run 8omhs on head but as stereo on the cab. the 4/8 omhs setting is in same position on selector switch for the cab.if you can help me out i would appreciate it.thank you for your time.

[defaced]

Run the head in either 4 or 16 ohms, and use the matching setting on the cab. Since the 8 ohm setting on the cab is stereo, I wouldn't bother with it unless you're trying to drive it using two different heads.

[Skeet Bonham]

would one selection be better than the other as far as performance and safety to components?

[Albert Kreuzer]

would one selection be better than the other as far as performance and safety to components?

No.
But you may notice a subtle difference in sound. Choose what you like better.