The type of car has nothing to do with it, not sure where everyone is from but X5s are as common as any domestic SUV where I live. Unless you're driving a 599 or any $250K+ automobile, you won't even get a second glance let alone generate any jealousy. I was just looking at the pic of the Audi vs. BMW billboards and noticed no less than:

4 Lexus (possibly 2 more in the opposing traffic)
2 Benzes (possibly a 3rd silver CLS in the far right lane)
1 BMW (possibly 2 more 5 series in the far left)

That's just one intersection in SoCal:
Autoblog



My .02 cents about the road rage incident:

You were in the left lane in an SUV (sorry, SAV) and some people in normal cars (i.e. subcompacts, sedans) just hate SUVs and minivans because they are tall and block forward vision, and the fact that a lot of clueless Moms driving them while gabbing on their cellphone impede traffic.

Regardless of the fact that you sped up, the guy behind you was already percolating for reasons that likely had nothing to do with you (this shitty economy has a lot of people on edge) I just get out of the way when I see people coming up behind me quickly and always hope that they do the same when I'm in a hurry (no such luck though)

It's best to just let it go.