As everyone has posted multiple times, The REAL KEY is to understand what condition is the vehicle in question and what does it need to be brought back to "specs". A PRE PURCHASE INSPECTION by a shop that knows X5's will provide a value well beyond the $150 - $250 you will spend.

Questions: Why this vehicle? Why not another year, model, engine size etc? What else is on the market?

Most shops will provide a overview of the vehicle and what is hidden underneath the nice wax and buff job.
On a personal note, A low mileage X5 with a V8 and a caring, thoughtful owner who maintained it (RECORDS PLEASE) will be a joy to own. All vehicles/owners must be verified before $$ changes hands. See Posting of those who did not and do not have the technical skills, available funds, nor tolerance.

A PPI and your own walk around and through testing of every switch and knob will be your best 1-hr spent. Better to know than to buy unaware...

I am sure others who post here regularly, will chime in on the value of a PPI.

What is unique?
The 4.8is is a beast. Needs hi maintenance and a tech savvy DIY owner. Suspension arms bushings take a beating (Front AND REAR)
Brakes big and expensive.
Trans life span is another weak point
Chews up 20" tires for dinner
Air suspension can be problematic, many solutions.
Big sunroofs, What can you say other than what marking guy thought that was important? Pull fuse and turn up the A/C!
Will provide more smiles per mile than anything else at double the purchase price.
Loyal owners who take pride in ownership.
Everything else is like your 4.4 except MORE Power, eats more, demands more and creates a thirst for speed....

If this one is a good one...Buy it. You will love the upgrade.

__________________

2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green