Maybe you need to target your shooting style and know what is the most important shots you want to cover. Unless you got 2 bodies, you are left with only one choice.
Another thing is whether you are paid to do this and if you are going to develop big prints. Otherwise I think the 16-85 would be quite a good choice. The 16mm wide can help you cover the group shots. The 85mm can be zoomed out for that extra reach. With the VR on the lens and some breathing technique, it should pull you through. Although it's not that long, you can later crop your pic and it will still give you a decent image. ISO 3200 is quite usable in my opinion. Good luck!