I came from a stage 2 MKV GTI myself, as others have mentioned before it seems like the 128i will be a better fit for your needs.
As for speed, the two don't really compare. I feel like the GTI was more jumpy down low but the 135i will just blow its doors off with a steady pull waaay past any speed the my GTI could hit. The only things I miss about the GTI are the seats, I had the Autobahn Package, and the DSG tranny. Hate it or love it but when driving the quickness of the DSG was amazing.
Cobb AP || AR-Design Downpipes || aFe DCI || HPF Exhaust || VRSF Front Mount || ER-Charge Pipe || Tial Q