I average about 22, and that's with a fairly heavy foot (mine is still fairly new to me, so I have a tendency to zip around traffic alot). Most of my driving is in city, but about 3-4 days a week I have to hit the interstate (70 mph) to get where I am going. I haven't taken it on any noteworthy highway distance so I can't say much about that part.
"It ain't about how hard you can hit, it's about how hard you can get hit, and keep moving forward. It's about how much you can take, and keep moving forward! That's how winning is done!" --Rocky Balboa