If you want to run ~1.2bar of boost then you definitely want to go with different pistons for lower than 9.5:1 CR, unless you want to run around on $10+/gal race gas all the time.
Are you still using the Motronic? If so, I'd tend to think something around ~8.0:1 or 8.5:1 would be good. Much lower than 8.0:1 and you'll start to loose a decent amount of response and low-end power. Hopefully someone with more experience will chime in but, those are my personal opinions. I believe my Carrera is either 7.0:1 or 7.5:1 (Mahle low CR pistons) and I'll say this much, the car is laggy and has crappy low-end performance considering the displacement though I plan on big boost so I'm sticking with it.