J.H.
Mythbusters did an episode of this.
http://en.wikipedia.org/wiki/MythBusters_(2004_season)
Scroll down to Episode 22. It stated that if you're under 45 it's better to have the windows down, and over 45 windows up with AC. (I think that's what it was. They revisited it, and I can't find that one.)
So it sounds like you're happy medium is not only a great compromise but it saves gas! (And with gas as expensive as it is, we need all the help we can get right? hehe)
I'm a windows down all the time kinda gal. I've finally found my style, which is a 50s/60s pinup look (kind of rockabilly). When I'm driving, I wear a scarf around my head (which also wraps around my neck) and my sunglasses. My hair stays in place and I look stylish! Problem solved!