You raise a good question but the answer to that is not going to be practical to give. I can only hope to give you some food for thought.
First of all, backpressure is never a good thing. However, since backpressure exists, systems are designed to account for some backpressure and therefore removing backpressure can have a detrimental effect in certain cases.
People often confuse backpressure with exhaust velocity and efficiency. Since it is very difficult to measure exhaust gas velocity at all points in the exhaust system it is easier just to refer to back pressure and not address the real concerns.
The key with exhaust is to maintain good velocity so that the gases get out of the pipes as quickly as possible without losing too much energy. If the exhaust gases have the opportunity to cool off and subsequently slow down too much while still inside the pipes, then energy will be required to push them out. There is also the issue with maintaining airflow in the cylinder that works in cooperation with the camshaft profile. If a motor is simply operated only in the rpm ranges that the camshaft was designed for, this is not such a problem, however, when the motor is operated away from the ideal operating range of the cam design (that includes most of us) then it becomes relevant that we match the exhaust system to the driving style.
One small example of this is if you have a cam profile that is timed for high rpm running and lets say you install a set of long tube headers on it that are tuned for low rpm use, you will find that the increased scavenging effect of the longtubes at low rpm will draw unburnt fuel past the chamber due to the large overlap period of the high rpm cam design. Then at higher rpms where the cam profile is working ideally, those same long tube headers that were designed for low rpm torque will create a restriction and the motor will end up being inneffient at low rpm and weak at high rpm. Hence matching components is a science that we cannot begin to get into here with these cars and our limited resources.
In the case of our stock motors, they do not have much overlap in the first place, so there is no danger of drawing raw fuel into the exhaust. The only danger we have is making the exhaust too big so that exhaust velocity drops and backpressure actually increases.
For any and all stock or mostly stock SC's, 2.25" headpipes are quite adequate and it would be of benefit to move the converters as far downstream as you possibly can. 18" to 24" would be best. Then maintain cross-sectional area of your pipes out the back. Straight through mufflers are preffered on any boosted application. A 2-1-2 design will be more efficient compared to a true dual design. Maintaining velocity throughout the system is very important.
As for the intake in front of the supercharger, bigger is better and that is about all there is to that. The supercharger actually regulates flow through the motor, so big or small on the intake side will only have a marginal effect on boost levels and will have no effect on driveability or mileage.
Regarding the blower, I feel that a stock blower should not be overdriven more than 5% or perhaps I should say no more than about 14psi. Once the blower has been ported it will have lower outlet temps that allow you to run up to about 16-17psi but then a bigger intercooler should still be used.
One of the problems that we have in this community in really quantifying some of these theories is that we have had such a hard time getting these cars to run consistently regardless of mods or upgrades. What has worked wonderfully for me and supports my theories has not worked for other people for whatever reason and so establishing a firm guideline is very difficult. People simply won't agree on what works or doesn't.
For what it is worth, some of the best computer modelling suggests that our motors should make good power up to 5500 with the stock camshaft. For some reason our motors peak at 4600. Obviously there are some other factors other than intake and exhaust parts that are standing in the way.