I can not say much about an SC but i have had stainless fitted to all my previous cars (not my current Subaru Forester). Yes it makes the throttle response a bit crisper, improved MPG? possibly but not too noticeable but that could be because of the sportier sound that makes you drive a little more spirited & so offsets the increase. obviously a stainless system has the potential of being slightly heavier but should out live the car. You will probably have an increase in sound. some of my systems have had tailpipe inserts that do quieten the system down.