Go 3.0.
Upsolute Chip 220/221 stock + 15Hp/20lbs = 235/241
Add Supersprint performance exhaust = +3 to 5%= 245/250.
Minimal risk modifications. More luxury, bigger stock brakes, etc. etc.
Yes, you can highly modify the 1.8T engine, and don't forget the transmission to go with it, to insane performance levels. At a cost to your pocket, and to the longevity of your engine.
I like the power I have now with my 3.0. In a year or so I will upgrade to an S4 or an RS4 if they finally bring one out.