As much as I love Avant Garde metal (it's my favorite genre), I could never get into those guys.
Right right. My favorite category.*
But where do you draw the line between progressive and avant-garde? etc
etc etc etc
Yes.
Progressive tells you it will either be a bunch of wank, something influenced by 70s prog rock, or something that's actually being progressive ie avant garde.
"bunch of wank" and "avant garde" are meaningless descriptions in terms of what the music sounds like, so really you're saying the progressive label only tells me something in the cases where the music is influenced by 70's rock.