LONG Exhaust ? - I know they suck

Have to start off by saying it's been a while - sorry.
The truck hasn't been running in over a year (complete race build) so I haven't been thinking about motor mods for a while. I am finally getting to the point where the front end completion is in sight, so that means it's almost time to build the motor while I build the rear suspension.
I know there are a LOT of exhaust questions around here, and yes I searched before I asked but I didn't find the answer I want - plus my situation is a little different.
Anyways - here it goes:
Are the exhaust systems on superchargers like turbos in the way that bigger is always better? In turbos the more free flowing the exhaust is, the more power there is.
I know the stock SC exhaust sucks, and that a more flowing exhaust is essential to run a 10* pulley, but how open is needed? Because I am doing the 100% custom thing w/ the truck, the exhaust will be totally redone. I am starting w/ 3.8L mustang (tubular) headers because the truck will still be smog legal so no true headers will pass smog here in CA. I have 3" cats that will only be in during smog tests (cats don't last offroad - too much vibration) and 2.5" hollow cats that will be in the rest of the time.
This is where I start to get stuck. My 1st plan was to go true dual 2.5" with H pipe to mufflers (spintech, borla, or magnaflow - haven't decided) and out. But then my buddy told me he has some stainless 3" tubing he will GIVE me for the truck, which makes me really consider a complete stainless exhaust, but it will have to be 3". This made me consider going dual 2.5" into 3" just behind the cats w/ single muffler and a 3" out.

I will NOT be running a resonator as I didn't have one on the truck before the rebuild and it was waaaaay quiet (stock cats w/ 2.25" pipes into a single 2.5" flowmaster). Is there any point where the exhaust becomes too open on these cars? I will need 75% of my power band to be in the 0-60 mph range for the off-road this thing will see, and I know bigger pipes loose low end grunt on N/A cars - is this true w/ SC's?

Thanks in advance for any and all opinions. Steve

TTT - Anyone?

how big is the trucks engine?

btw a turbo set-up differs alot from a supercharger set-up ( u probably already know that). The turbo will actually want a bigger exhaust then most supercharged cars due to the fact that the turbo is a part of the exhaust itself....and the quicker it can move the hot air out...the better. The sc is just on the intake portion of the engine and as a bigger exhaust is better for the tbird sc's i would assume there is a way too "overkill" and lose alot of torque.

anyways , more info on your trucks engine would be great

Isn't the problem with too large exhaust being the back pressure?

Does anyone know what the back pressure should be? Or what ranges are okay. I'm pretty sure a couple of psi is optimal from other reading, but this isn't something everyone can measure easily.

The engine in the truck is out of a 90 SC - which is why I'm on this board. I've been here for a while actually (guessing 2 years now) and realise many guys on this board know these motors WAAY better then I.

Anyways - not much done to the motor yet, but I will begin soon. I will be porting and polishing heads, custom front mount double IC, raised SC top, 10% pulley, o-ringing the deck, full exhaust, possibly a cam re-grind and not sure what else (open to suggestions - and trying for 300 HP at the crank)

I understand the difference between turbos and SC's, and I realise turbos are part of the exhaust system so bugger is better. I have also heard that this same theory of rapidly removing exhaust gasses works for SC's but I wanted to confirm that. I understand that you can have not enough back pressure on N/A engines and loose torque, but I am wondering if it is the same w/ SC's.

I guess it all boils down to "what exhaust is commonly run?" After reading post after post on exhaust I think most of the guys here are running 2.25 or 2.5" into dual mufflers (magnaflow, flowmaster, borla, etc.). I'm just wondering if some of the big boys (meaning high HP) are running 3", and if they suffered low end power loss because of it.