Not side by side... but my experience is as follows.
I bought the Demeter and used it for one gig (Moollon P and Barefaced Super Twin) and then sold it. It sounded great at home, but couldn't hang on stage. Granted, it was a rock gig with amps and a full PA... but I was completely reliant on the monitors and the house mix. The amp didn't even need to be there.
I bought the Sisma and it became my go-to amp for almost every gig. I consistently used the same P, but now have a Super Compact. This is my perfect rig.
I love the Sisma so much that I am considering spending the $4k for a Volta. I don't have a need for an amp that powerful, nor do I have $4k to just toss around. So, it's not a likely proposition at the moment... but if there was a need...
As info, my previous go-to was the same Moollon P into a Noble, into the preamp of a Darkglass MT900 v1 (EQ set flat, but utilizing the gain structure) through the Super Twin (all pictured in my avatar). I generally plug straight into the amp without the use of pedals (though I'm not opposed). I generally played blues with this rig.