Periodically take off the intake pipes for the turbo and look for signs of pooling oil (a light mist is ok). Also check CAC/intercooler for accumulated crud. If both those areas are pretty clean, you probably do not need a catch can. If you DO find buildup, clean it out, and check it again at the next oil change, or 3K miles whichever comes later. If no buildup, then I would say it is good to go.
The only ways I have seen for reducing/eliminating soot are
a) higher E fuel (mix with E85), E15 or so
b) an MDesign CAI
Use Top Tier fuel.