1. Our "enemy" is the C63 AMG, not the E63. This car is enemy to the M5.
2. At this power level, I really think you need AWD, especially in a large front engine sedan with relatively narrow tires. That's where a car like this will hammer an M5. M5 simply can't put its power down effectively enough. I know RWD will still give you a more dynamic feel, but in these bloated, heavy power barges, what difference does it really make? People don't buy these cars to take them to the track. Even the vast majority of M5 owners will never track their cars.
3. I have never been a huge fan of MB looks. There are a few models that are nice, but their styling tends to look dated very fast. BMW designs are timeless. Even a nicely kept 12 year-old e46 M3 still looks hot.
4. Keep in mind, that we are splitting hairs here. At this overall caliber of car, no matter what you buy....S/RS cars, M cars, AMG cars.....they are all really pretty good.
Audi S6 * Audi S3 * Porsche Cayman GTS
--Former BMW M3 owner