Robert S. said:
I have a Marshall 1/2 stack and I run off of only 2 of the 4 speakers at 8 ohms. It may be all in my head but I think that my JCM 800 head sounds better at 8 ohms. So you may find that running two 16 cabs for a total of 8 ohms sounds better than running a single 16 ohm cab, even though both ways are mono.
My main gigging amp is a Mesa Triaxis/2:90 rack that I run through two 8 ohm 90 watt Mesa 3/4 back cabs. This is a true stereo rig and the difference in tone is huge. For one, both sides of the 2:90 as well as both cabnets have a slightly different tone so the tone is a sum of both sides. Also, I run a slight 4 voice detune panned out across both channels with different ms delays which acts somewhat like a doubler.
Most of the clubs Im playing in lately run stereo PAs and even though the sound guys whine a little from time to time I still have them hang 2 mics for me, one a side. There is a very big difference in tone and it's very apparent both in rehearsal and in live situations. I also do some panned octave stuff and a panned tremolo/leslie thing that is stereo dependant as well as some panned 3 voice harmonizer stuff and both channels need to be there.
At 90 watts a side, I get stereo imaging whether the PA is mono or stereo and you can definately hear it live.