Hi,
In my opinion CIS is the way to go.(I am telling you this because that is what I am doing right now
after a long research )
If you find a Turbo CIS (from Volvo, Saab, etc) that will match you CCs its even better and should work well.
People say that 'if you want to go turbo go t1' if I tell you that a friend has build an over 160hp 2L Turbo CIS street engine(low boost) with all stock type4 components that means that t4 can be turboed with little problem.I've not done it yet.
What I do like about the dual carbs is the Looks! and the SOUND! with FI, even with a full flow air intake system(K&N) the sound is not the same...neither the pure boxer look...
When it comes to power, opinions are various about CIS and dual carbs.You will never know for sure until you test them on your own engine. Thats my opinion..
Try
www.cbperformance.com for NEW vw turbo FI parts.
good luck!
Martin