I have a 318is, 1995 model. I'm thinking of replacing the exhaust system with a stainless steel upgrade muffler system from either Billy Boat or Remus. They are both pricey and they both claim to improve performance and give the car a 'throaty' exhaust sound. I'm more interested in improving the 318's slightly mushy uphill performance than in the 'cool' sound they make. Anyone have experience with this issue?