I was wondering about what the HP and Torque increase and increase on MPG would be on the following items for the 8100 Vortec engine?

K&N fuel injection air intake?
Headers? JBA, Edelbrock, Thorley, Gibson (wich ones are better?)
Dual exhaust system(cat back) with dual(back or side exit) from Gibson,Flowmaster,JBA,..
Hypertech programmers???

Just wondering what you guys with the 8100 vortec engine have tried and what kinds of results you have seen.