If you was to import it wouldnt you have to pay the extra tax or some bollock$ like that?
And remove the speed limiter, as some US states require a 125mph limiter.
....Is it easy to remove? 
I don't know!
I never bothered with removing it on my last S4, nor my present RS4 - but then they were known to be a little lax from the supposed 155mph limit. When the B6 S4 was out, genuine top speed tests gave the limiter kicking in at 161mph, and I had 165 showing on mine. Even down some rather, large long and empty hills on the french autoroutes wouldn't get it to budge over that, though on the flipside, it would still pull that going up hills too.
I've had my RS4 upto 172 on the autobahns, but with only 4k on the clock, the engine still felt slightly tight, and not full loosened up.
I do know that Audi, just like all german cars, have very accurate speedos - overreading by 1-3mph. Can't say that for cars from a certain rice country, nor those with a blue oval (though Fords are better than they used to be).
