[Ender]

Originally Posted by Tinman

Air intake system utilizing fresh air from outside the engine bay, 1 point
Many people have tried this and it's hard to make worthwhile improvements on the stock intake, turbo or not.
Catalytic converter deletion, 1 point
Should be a huge help, do this for sure. Cats, stock especially, make the engine feel like it's pushing silly putty through a straw.
Cat back exhaust, 2 points
Pretty pointless if you aren't going to pull the cats. If you do pull the cats you would probably gain more from a good header on NA (they are very inefficient), and on turbo if you pull the cats then you'd have either open or a downpipe anyway. A catback is especially helpful in creating power on turbo applications.
Header, 2 points
See above ^^^
Underdrive pulleys, 1 point
Maybe for reliability. If you're revving really high a lot your water pump may cavitate and you can overrun the alternator, but I doubt you'd see much power gain from it.

Any actual dyno numbers would be greatly appreciated.

Comments in red.

I actually had my first dyno run yesterday. Poor conditions, it was cold and raining, and despite replacing my turbo-mani gasket two days ago it might already be leaking again... grrr.

Relevant list: untuned 13Bt, Rtek 1.7 ECU with 720cc secondaries, 10psi max boost using a cheap manual boost controller and cheap BOV (that may or may not leak some...), open 2.5" dp to a y-pipe splitting to two 2" pipes with a muffler on each, no emissions, manual steering, A/C still installed.

Pulled in 4th gear.