Aside from the 20hp, there is no other performance advantage. I put the $800 Cobb AP in my car and had probably 30-40 more hp than an IS. That being said, I would still get the IS for the wheels and exhaust. If it was between the N54 and N55is, I would go N54 all day.
The views and opinions expressed in this post are those of the author and do not necessarily reflect the official policy or position of Bimmerpost.
2010 S4 Current | 2010 BMW 135i Retired | 2006 Lotus Exige Retired