Here are a couple things to consider:
1. If you have an open bar, you can also close the bar 1/2 hour before your reception and 1/2 hour during your dinner or lunch. If you do this, you will save an hour off your bill per person. So instead of a 5 hour package, do a 4 hour package. Most people are used to a "last call". Also, during dinner.. just warn everyone that the bar will close for 1/2 hour and get their drinks beforehand.
2. Another thing.. if you do have some big drinkers, and there's an open bar or BOC, people tend to set drinks down half full and get another one. They go dance, put down a drink, forget where it is, go get another one.
Just really think about your guests. With mine, there was no option but to have an open bar. None. I had big drinkers and I know I saved money. Just really asses how much people drink. To them open bar is open bar - they don't know if it's a BOC or open. Some people drink more too if it's free to them. Hope this helps somewhat.