4.8 overkill exhaust questions

[Skylark]

I'm building a cammed supercharged engine for my 93 ecsb. I have many projects that I'm doing to the truck and I'm thinking about just dropping in a 4.8/T56 that I have into it and driving it. The exhaust consists of schoenfeld headers, 3" true duals with an h pipe, magnaflo mufflers and then run out the corners of the bed.
What will i lose by having such a large exhaust? Would dropping the size of the pipes to 2.5" right after the headers and going back to 3" just before the h pipe be of any benefit?
I'm honestly not caring about performance, I just need the truck up until about this time next year.

[chvy=power]

id say it would run better with the 3'' no doubt. Itd be crazy to drop back to a 2.5" IMO