To the OP, sounds like you know what you're doing, so perhaps an X is for you, but like others have pointed out, this particular one isn't it. Less miles, lower price, and a warranty can be had.

I have lurked here for months, and frequently I can relate to Repoman's travails. I also happy for the crew that really loves their X. I want to be a fanboy, and a slight glimmer of hope for that experience remains. I am accustomed to rendering TLC to vehicles that need it, but this one is trying my patience.
In 2001, I was at Bluegrass BMW for one of those breast cancer charity things. I had driven pretty much everything in the fleet, including the scary fast 5 series wagon(540I?) that nobody else wanted to drive, and was waiting for the 7 series to return, when the X5 rolled in -- a 4.4, black, -weird - all the other cars where Titanium.
I hop in,fire it up, and by the time I had blasted it on and off I-24, I vowed Someday I Will Own One of These. It was the all-of-a-solid-billet, vault-like feeling, combined with handling & power.

Fast forward to October 2008. Wife barrel rolls her beloved 300M. She walks away with minor injuries. Great car car, BTW, 204K on it, super reliable, motor or tranny never apart for any reason. Would still have it, if the roof & doors handn't been "Jaw-d" off.
Wife drives my 14 yr old Jeep Grd Cherokee, while we figure out what to do. Hates the creaky handling, but does mention how it's much easier to load our infant son into the back seat. The memory flashlight goes off -X5!! "Say, how 'bout a BMW?" After lots of internet searching & comparing, viewing what looked like good candidates, I spot a 2003 4.6Is with 62K at a non-BMW dealer nearby. I learn that this is the hi-po model for that year. (Duh! you all here are sayin') We drive it. We like it. We pay too much, rationalizing it with - "we need to get this search over".
Drive it home, it's cool & scary fast, for a large vehicle! Great fun taking family and friends out & snapping their necks back. I live in a cold place. How bout some defrost? Hmm....I don't hear a fan. Turn them knobs & switches & dials. Push numerous dash buttons. Nothing. Well, it is a BMW, perhaps it's so sophisticated that you're not supposed to notice any air blowing. Hand me that ice scraper-need to scrape off the inside of the windshield. Oh, and have you figured out how the wipers work? no, didn't think so. It CAN'T be non-functional? "Hey, you need a FSR".
Whatizzat?? Ok, fixed under 30-day used car warranty, but no dice on the Rain Sensor, not essential for driveabilty.

Wife backs out of garage, drives it 300 feet down road, turns around, comes to find me and says "what do you suppose Trans ailsafe Frog means?" Huh?? Frog?? Bad pixels, can't see it clearly. I search the net, hit on this site and read the very bad news -- tranny is very likely toast. Shift into gear, take off, drive a short distance & WHAM! Vehicle is in what must be 4th gear, no power. I am lucky compared to some, at least my car will move. Others have had complete immobility. $4500 and five weeks later, a reman ZF is in place. Works okay, but doesn't have the off the line response the old tranny had.

This vehicle has taken me to school. It throws codes like a Major Leaguer. I've learned about switches, solinoids & fuses. About smoke tests & hoses & coolant tanks & bearings & belts. And The Water Pump, oh yes, -it decided to sieze on a cross-country trip & left me, wife, toddler son, biach-y sister n-law & teen-age niece stranded in Cleveland, with the feral pack of humanoids malingering about. I actually like Cleveland, just not that particular spot at that particular time.

Did it ever enter my mind to question BMW's reliabilty before I bought my X? Never. Now I do. I intended to purchase a safe, reliable, and fun to drive vehicle primarily for my wife to tote the boy in. I am certain that the X would protect them in a wreck, but I am on full alert for the call at 2 AM, telling me she's stranded at work because it won't start
.
It's been about six weeks since something has gone bad. The bitterness is wearing off. I am falling in "like" again. A wash, a wax, a spring drive, who knows? Perhaps my TLC is working. Or the Flux Capacitor will take a dump.