I almost did not purchase this car after reading what Edmunds and alike had to say, but luckily did after driving both the E63 and M5. They are definitely fast but so is a ZR1 corvett or a mustang! Point being, Audi owners have more in mind than pure horsepower. It's the ability to have a car that handles under all conditions and environments, and do it in a way that doesn't say look at me. And seriously, the engine is a thing of beauty! The M5 will take me out until it starts to rain..he'll be in the ditch and I'll be eating dinner! I have seriously considered getting an R8 but can't come to grips with giving up such an all around wonderful car.
This is my 4th Audi and by far my favorite. You can't compare this car to the M5 or the E63, That's what the RS6 is for (We won't get the current 570bhp in the states) For those of us that know about Audis, this car will blow away any E500 or twin Turbo 550i and you will look better doing it. This is the best S I have owned. I had the 2001 S8 and that was a blast too.Until the 2011 RS6 comes this is the next best thing or the 2003 RS6.
Don't kid yourself, this car gets expensive fast, expect no more than 17mpg unless you do a ton of highway miles. Cheap repairs are 2k+ a set of tires is easily 1800. It really should be babied to keep up appearance and performance, plan for 400+/mo. If none of that makes you cringe, then I highly recommend it. It will keep pace with if not outright decimate most cars out there, and happily put domestic upstarts to shame, while looking so much classier doing so. It handles beautifully, even performs drifts well, especially for a heavy luxury sedan. Every day with this car is a treat, it makes every mile so much more fun than my 08 S4. The onboard tech is very impressive, and for someone with back problems, it's extremely comfortable, even on very long drives (8+hrs). If you're considering this car and have the desire to spend the money on it that it deserves, just do it. Anyone who says the 3L turbo A6 is comparable is simply wrong. This is an entirely different beast.
This car is absolutely amazing. The Led lights are stunning. The white and red interior dashboard displays are amazing. The sport seats are very comfortable and keep you strapped. Everyone that sees this beautiful and yet understated beast knows that there is something very special underneath the hood. I might as well replace the stock hood with a transparent hood to see that Lamborghini derived V10 beauty.