Well, obviously, the magnificent X3 xDrive35i won't go anything like the M5 does so test drive first and see if you can live without the BLISTERING acceleration. That said, the 35i does shift!
Would you ever take the X3 off road? Really? Be honest! Sure it will be better than the 5er in the snow but think of all the days in a year and give me a figure of how many days snow is on the ground. The X3 is a great car but the M5 is awesome and the E60 will always be one of the all time greats.