I'm interested in this thread too as I'm planning on doing a head pipe soon. So far I'm going with V&H Power Duals to go with my existing 4.5 HO's. I've heard that set up and like it...and the X pipe does help low end torque.
just switched up V and H power duels for dresser duels ran Rinehart 4"on both. The dresser duels look better and sound much stronger then the power duels people say some low end is lost with the dresser duels I did NOT feel any loss of power. I just had a baffle come loose and im posting that story next