exhaust opinions

[sneakyfast]

Ok gents I have a 73 with a 383 stroker that the Po has a 3 inch running that dumps right behind the cab and is loud enough to rattle your fillings lose. I'm considering running 2.5 if it doesn't kill my power. Its a daily driver so

1. Will I notice a power rob? Ive seen some opinions say I shouldn't notice a difference until the motor is running 500hp but that doesn't sound right
2. The Po also is running full length headers, should I change these to shorties at the same time or does it make no difference?
3. I used to love the sound of flowmasters but they have a bewildering number of choices in 2.5 inch. Any recommendations?
4. He has a 950 cfm crab which seems huge to me but will I need to change that out to?

Thanks guys and when you reply lets pretend I was raised in a public school and have been out of cars for many years