Replace it all and be happy as one part replacement will always magnify the slop that exists in the upper arms.

Normal wear out of service for the rear suspensions for V8's is 60K. The lack of torque on the I-6 bangers allows much longer in service specs.

As Andrew mentioned, the rear ball joint wear out is tough to determine. If you pull them (actually it is push them) out you will see they are toast long before the replacement occurred.

My own 4.8is rear arms were toast at 62K. Front torque arms at 42K. Too many hard stomps followed up with heavy braking. Yes, the V8 tires wear out real fast as well... I think X5 V8's actually eat tires.

I believe Andrew is on to something regarding the rear suspension part wear. On hard acceleration they toe in VS heavy braking the push is to toe out. This action pounds the upper arms in the rear while eating alive the front ones. Wonder what the engineers found leveraging strain gauges during development? The results gave us the same parts for V8 and I-6 in the rear....

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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