Boy, I can definitely relate. I debated long and hard when I was ordering my '08 X5 (do I spend close to $7k extra to get a similarly equipped 4.8i version or not) and ultimately decided to go with the 3.0si well loaded build with the justification that I was saving money on price and eventually gas. Even though I couldn't be happier with the X5 3.0si I have now, the notion of regret (for not ponying up for the 4.8i when I had the chance) continually haunts me especially when I need to dig in for that extra oomph in merging or passing.

Like you, i've debated trading up for CPO'ed similar year and equipment 4.8i version or even going with a brand new V8 model long and hard but I ultimatley found peace in knowing I can wait it out and get the biggest engine when I'm finally ready to trade her in.

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Cheers,
Tae
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2012 BMW 750i XDrive Sedan (Current)
2008 BMW X5 3.0si (Current)
2011 BMW 328xi Sedan (Past)
2008 Audi A4 Cabriolet 2.0T Quattro (Past)
2006 Audi A4 2.0T Quattro (Past)
2002 Acura TL-S (Past)
1996 Nissan 200SX SE-R (Past)