I might as well as add my Dinan $0.02 as well. My X5 and e39 both had Dinan S1 packages. Dinan stuff basically does 3 things. 1) Make your BMW a little more unique, to where BMW SA's, and BMW Fans with give you the thumbs up because how many Dinan BMW's do you really see? 2) Empty your wallet. 3) Give you very small gains in HP and TQ.

Now, if you are looking to spend $3K and get significant performance upgrades than Dinan stuff isn't for you. Short of a SC you aren't going to see any real gains. You may see a +15 in both HP and TQ, and its up to you if it is worth it. I spent it on both cars and loved it, and would do it again if I had a BMW right now. But to each his own. Also, if you are planning on selling your X5 in the next 2-3 years I wouldn't do any Dinan stuff as you won't see any bump in selling price because its equipped with it.

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Jeff
Current:
'07 Jeep Wrangler
'06 BMW X5 3.0i

Former:
'12 WRX; '08 WRX; '06 BMW X5 4.8is Dinan S1; '02 BMW 530i Dinan S2