for the M5 replacement, i ordered the X6 50i, Space Grey with Black Nevada with Aluminum trim.
i drove the 35i (basically feels the same as X5 35i), 50i, and X6M before making the decision on the 50i. i found it's perfect on both world. i could've settled on the 35i especially it'll be a semi-car for wifey. but since i'll be driving it also so i guess the extra power on the 50i won't hurt.
i love the X6M, but i can't justify the extra cost over the 50i. during test drive, i could tell it's fast but not what i expected. honestly i excepted to be faster. i did put it in the M mode but the pull never surprised me. the sound however, is pure sickness. i wish the 50i sounds like that... i guess at the end it's still just a SUV, regardless BMW call it a SAV or whatever. a SUV doesn't have to be rocket fast, and i would be more comfortable driving/pushing hard in a true sports car than a SUV.
on the side note, i also checked the MB GLK350. i thought it could be a perfect car for wifey, at the same time add some variety to the line up. it's a nice compact SUV, but the lease number never makes sense on the Mercedes, as well as Audi. i think it will still be a candidate if we decide to get another car later the year, but i'd rather let her have the X6 so i can go buy something fun later!