I rented a BMW 438i for two weeks a few years ago. Surprisingly little wind noise even with the top down and you can reduce it even further by putting some windows up.
The only problem was that with the top down there really wasn't much space in the boot.
It was one of the most enjoyable cars I have ever driven. But not exactly economical :-)
Edit: Forgot to say that this was in the UK and we drove from Dorset to Northumberland and back with lots of places in between.