If you have an 850, be prepared to be very disappointed with the performance. While it is fast for a sedan, it does not perform as well in the real world as it looks like it would on paper. With the big V12, it should haul, but even the heavily modified ones seem ponderous. Not trying to bash the car - they are one of the best looking bimmers and are very classy - but a modified NSX will be a LOT more fun to drive. Every one I know who bought an 850 sold it within two years.
Again, not trying to bash the car, but it is a pattern I have seen many times and one of the main reasons I bought an AMG instead of a V12 850.