Limit is anyone's guess, had a few lads break rods around 260-270lb mark on TT and Audi forums, other have not had any problems. At the end of the day its the torque that kills then especially if its delivered harshly. Stock pistons are quite good. The real question is what are you trying to achieve as this will decide on what will need to be done and how much it will cost. Are you uping the RPM limit, after a certain bhp driveshaft issues become a common issue, then there's the valve-train.