a set of 4-1 extractors will give better top end power but often result in some low end loss. 4-2-1 will give a broader spread in the power band but wont give as much top end gain. so basically 4-2-1 is more suited for everyday driving. it sounds like the guys at best mufflers dont know squat. if your going with extractors you have to replace the rest of the pipe or it will just bottle neck and the extractors wont do shite. 2" is fine. no way is it too big - if those guys reckon thats too big for a car which is raced, i'd say they are racing in their driveway. some peeps go with 2.25" piping as it can give slightly better top end, though often with slight losses in bottom end power and torque. really have to decide based on how you like to drive.