X & H pipe vs straight dual exhaust

One the other side...
My muffler guy recommended against any kind of crossover. My car of course is a completely different ticket than a big block with headers -- 273 4bbl with manifolds and 2.5" back to dual Super Turbos. I don't think HP/torque was even considered -- he thought it would kill the sound... not to mention get in the way when monkeying around underneath. He seems to have a good idea what I'm about :)