It is quite the same in Miami as well, as I know I was certainly surprised on my first travel there back in 2004. The most-recent trip however was far less surprising, but the ol' Michigan roots tend to kick in at various times to tell you to slow down when it is completely unnecessary.
It may be interesting to note that 90 MPH feels far less-safe in a convertible Chrysler Sebring than it does in a Lincoln Towncar, however, they clearly are for different purposes.
That is one thing that I love about luxury sedans, always good for traveling at high rates of speed relatively comfortable. Then again, spend a few extra bucks in any class of car, and you're bound to find something better. Thats why VW lead the class for so long, benchmarks for all with the Golf and such.
I'd love to have the CTS at 90 MPH through Miami, it would be fun, but it would likely look a lot better through SoBe at night... Preferably in black with the chrome and the lighter colored interior.