What could I gain by swapping to longtubes?

[Grn92LX]

Does anyone have any dyno or track mph #'s before and after from swapping from shortys to LT's, preferably on heads/cam 302's. I am thinking about it. LT's should also quiet my car down some and less interior drone, right. I figure with the $$ i'd spend on a quieter cat back, I could spend a little more and gain power and reduce noise a little while retaining my flowmasters cause I like the sound. I dont want mac's, but am looking at BBK's, but anyone else make a nice affordable LT besides the summit/flowtechs?

Also by swapping to LT's, how would that affect the overall tune of the car, meaning, does the better exhaust scavenging require more or less fp or timing??