For me, it's all fairly simple: if I can 'reach around' the neck with my short-ish fingers, I can play the bass(thus eliminating P's); if I 'twiddle the knobs' and get a sound I like, AND can carry the thing, then it's a good amp. I leave the possible "ehems" to the rest of y'all.Can't say i do as well.
[ that's Southern for ...uh....er...Y'all.]
Edit: Hmm. That lower volume thing just might be why I was never knocked out by my mid 70s SVT/810 rig's tone. It did move a lotta air, though.

. There's still no need to go into the PA, though.