M5 and 540 are obviously not the same cars and play to different folks. You can speed up a 540 to wax an M5 but there are more things to the M5 than 540. 540 is an awesome platform, don't get me wrong. I owned one for three years and I loved it. M5 is just the next step. You are correct about the resale. If you can enjoy your car then you effectively amortize the cost of all theupgrades needed to get M5 performance wise. Most don't keep it for very long, but if you can, then the ultimate sales price really is not that big a deal. Cheers.