search for Turbo dynamics , there is a review on stage 1. i have stage 2 which is IMHO the only stage you should consider (both comp/turbine are bigger) . Quite expensive.
You could choose instead RB turbos or Vargas.
07 335i AT - TD St.2 Turbos - COBB (Custom Cobb mapping by http://www.protuningfreaks.com/) - JB4G5 ISO - Okada Coils - NGK 5992 Plugs - E85 Walbro - Injen Intake - Helix IC - Snow Stg. 3 - Stett CP - AR DPs - midpipes 100 HJS Cats - Bastuck Quad - PSS10 - QUAIFE LSD - BMS OCC - Forge DVs - AR OC - ALCON BBK - M3 Chassi - Dinan CP - Velocity M rear Toe arms - Advan RZ-DF - Level 10 AT upgrade - Alpina AT Flash