Just a follow up to your questions, the guitar vocal gain is not super high, just a little more than others.
Using a Senn 935 helped a lot, but he still wants more isolation from the drums.
His guitar rig is at a reasonable level, so the drums on stage will be the loudest thing, but I still don't believe they're too loud.
He is not in front of the drums - he's stage right. Stage is 24' x 12'-6" deep.
His IEM's are not of high quality - I failed to mention this.
I might revisit the gate, using some settings recommended in this thread.
I don't have an expander - wish I did now.
Right now I'm considering showing him the Optogate, but we have a lot of flashy-blinky going on. Again, we're not doing a drum shield.
He's a good sport - I'll talk to him about getting up on that mic and singing a little louder. Often, it's just when he talks to the audience where I run out of fader.