My very personal view...
Stereo will always sound "bigger" and more expansive and open up delays...but...that is not always advantageous, especially in a live situation.
In a band its important each instrument occupies its own sonic space otherwise sound is lost. I have found that the more effects and wider sound, the more there is that potential ( and it is only a potential).
I remember going to a friends gig and he had a new line 6 stack ( this is over 10 years ago BTW). He let me have a quick play before the band started, it sounded really good on its own...as soon as the band started up, it totally disappeared. It wasn't a volume thing, it was a the sonic space...
I experience the same thing back in the day, running a stereo set up ( ada pre amp, marshall 50/50 power amp, Quadraverb and 2 1x12 speaker cabs). Enormous sound on its own, lost in a band. I changed to a Laney head, mono with NO effects ( no reverb even) and the best sound in a band i've had prior to the KPA. I've therefore held that mantra. In a band I feel that its the tightness that gives the biggest sound, effects can add bleed.
Therefore for live, especially in a 2 guitar band, stereo is a disadvantage..