[Freon]

The turbine operates largely based on pressure ratio (absolute) before and after itself. The lower the pressure after the turbine, the greater the power and energy transfer from exhaust gas to the turbine wheel. So the less exhaust backpressure you have after the turbo, the better, at least in a steady-state condition. In general it should be good for spoolup and topend power. I.e. if you have 44psiA in the exhaust manifold and 22psiA in the downpipe just after the turbo and before the catalyst, you have a pressure ratio of 2:1. If you replace the downpipes with catless models and reduce pressure after the turbine to 19psiA, your ratio has increased to about 2.3:1. That's more energy transfer to the turbine wheel.

Things get a bit complicated (i.e. arguable) when you talk about shifting gears and momentum of exhaust out through the exhaust system as you briefly shut the throttle plate... I would hate to generalize here.

Rimas, your experience with lower boost with an intake probably has more to due with not being correctly retuned than anything. Boost control is a closed loop system with a LOT of feed-forward in the solenoid duty and whatnot. Changing parts can upset the tune a lot and cause it to perform worse even though you've made a largely positive change in airflow or design efficiency. The system is too complex to create a causative link from your experience such as, "adding intake results in lower boost".