I did this on my '04 3.0 and then moved them to the 04 4.8 when I bought it this year. I loved the difference when I put them on the 3.0 last year. I wrote a little review at that time:

• As you might expect, the thing is MUCH flatter in the curves. It feels like a much smaller car. I have the feeling this will get me into some trouble one day, but for now, it's a silly grin.
• I can drive it differently, but I really don't. It's a grocery gettin truck that I bought for baby haulin. When I am in it, this is my mindset. I'm no prude or anything, I just know that my fire breather is a 5 of another sort. I like this thing to climb over the occasional curb or lumber along full of wares from Home Depot. I've driven it off road both on purpose and by accident.
• It's a six. In order to REALLY take advantage of a handling difference this new to my experience, I have to plan ahead. Carry more speed into the offramp. Brake a little later than I might have otherwise for that 90 at the end of the road. Or hell. DON'T brake. With 315's on the back, the thing sticks.
• But, I'll tell you what I DO like and why *I* find this is a mod that's worth it. I notice that on the exit of a given turn, I feel more grip. The X5 is flatter to the ground and I feel the inside front wheel pulling me out of the turn. I felt it before, of course. That's one of the things that made me fall in love with BMW's AWD. But now, it's more pronounced. It feels awesome.
• Ride comfort is not noticeably discounted in straight line driving. It's a bit more abrupt in a rough surface turn- like over a railroad crossing for instance. But the thing is heavy enough to settle down pretty quickly.

Since then, I have driven the 3.0 immediately after the change back. It's still a great handling truck. One of the best for it's size I am convinced. The handling is what kept me in the 3.0 for 7 years and what moved me to the 4.8. Since I just turned 15,500 miles on the 4.8, hopefully I'll be in it for for another 7.

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