I went from an E53 to my current 2009 E70 N52. In my case power was not really a desire, since it is driven by my daughter much of the time. I like the relative reliability of the unblown 6. I've done the oil filter adapter (and cooler) gaskets and a belt tensioner on the "new" X5, but other than that it has been OK. I find it unbelievable that BMW STILL can't make a 6 that doesn't leak oil here, but at least it was easier to fix than on the E53.
If I want quick I drive the G8.