Re: Nominal impedance?
Actually there should be no drop in volume between 8 and 16 ohms, provided we are talking about an amp with an impedance switch set to match the speaker. (With a solid-state amp with 8-ohm output, using a 16-ohm speaker will cause a drop in power).
All else being equal, you'll probably find the 8-ohm combination a bit brighter, and the 16-ohm maybe a bit fatter. Gerald Weber has a good explanation of this in his latest book, Tube Guitar Amplifier Essentials.