I took these two shots a couple of days ago, having noticed about half an hour before sunrise that the sky might be going to do something. I didn't have time to travel far but went to a nearby hill overlooking the city. The first shot was taken about five minutes before sunrise and the second about five minutes after sunrise. I used a 3 stop reverse GND for both shots. The first was a wide shot to capture the sky and the second much narrower to home in on the city skyline with the sun just rising over the horizon. I wouldn't normally attempt a shot like the second but there was in this case enough haze over the horizon to filter the direct sun thus preventing exposure difficulties (not to mention sensor damage !). A good rule of thumb is if you can look directly at the sun without discomfort then it's OK to shoot it.
Comments welcome, and as usual, best viewing full size.
Dave