If you don't want to lose power, but make power down the road, then a 3.5" or 3" kit is your best bet. While chambered mufflers aren't the greatest for turbocharged applications, that logic really only applies to heavily modified vehicles with large turbochargers throwing down close to their peak flow rates. Unless you're planning on building some kind of monstrous truck, then your muffler choice should really only be based on what sound you need.