Bumping up your thread to see if there are any updates to either your X5 M or GT-R.
I am in the midst of getting a 2006-2007 M5, and I would love to add an X5 M for winter driving tasks like snow boarding, and add a GT-R for weekend/track driving in 2 or 3 years.
Any other advice on the M5? You pretty much stated it is a nice balance of most of the cars you have owned but does not excel in any one category, which confirms my decision of having an M5 as a daily for a big dude like me
(6'4 over 200 lbs)