not the same as the 540, I can tell you that the difference is SO BIG that I wouldn't dare to even compare the 2. I also have an 850i, and believe me, even with 300hp, there is nothing comparable. The M5 is so much different (although a BMW) that you don't dream of. I'm still learning to drive it (see my post below updating driving experiences thread-D.Arnold) because it is SO fast that your senses must readdapt to this speed machine. Unless, imho, you are an experienced track driver, a regular high speed coaster as I am that thought could drive fast on a twisted highway, soo realize that I knew barely how to keep the car on the road at limping speeds compared how encouraging the M5 is to drive at relatively high speeds. Acceleration is so massive that before you can think of you're doing 130 mph, and that approaching a bend that before you could negotiate at mere 80 mph, makes a hell of a difference. Strechs of road that were long enough for you to get ready to the next curve are now reduced to a garage driveway. Brakes are though the weak point imho. 2 hard brakings and they're gone. Upgrading could be something to consider. If you ask me, nothing can be comparable with the 840 (only that it is a BMW ride). Rgds, Marcelo