I have a 335is, my friend has an E63 650i. My car is much faster and more reliable. His engine overheats all the time if he pushes the car even a bit. (His engine has even blown once...) And his gas mileage is pretty bad too...
The 650i is a good looking car, but it's outdated now compared to the new line-up of BMWs, and I personally would never buy a car like that second hand.