From everything I've heard, nearly every "more agressive" system causes highway drone. Some guys are complaining of headaches after only an hour of highway driving with other systems. I'm not going to list system names since I think it's a matter of opinion and don't want to whizz on anyone's personal preferences.
Corsa is the ONLY system I haven't heard anyone complain about highway drone. It may not be as agressive a sound as other systems, but the performance increase, improved sound and lack of drone are enough to convince me. Cheapest I've seen the CatBack Corsa for the SRT is $1305.00 - online - and then add installation costs. Lifetime warranty makes it worth the price.