You should go through the Mayhem build thread. Mark and I believe Brian Thompson, who built the engine, really give a lot of great info on heat management with the roots style blowers.
Maybe lag was the wrong term to use when talking about the Pro-charger but it's not as quick as a roots blower. I much preferred driving a Magnacharged vette to the Pro-charged ones even though the Pro-charged ones made more peak power typically. The torque band on a roots style blower is a lot better for street driving too. That's what really sells it for me.