If you don't have time to experiment before the event, buy more rolls than you need, and shoot an extra roll AFTER the event in similar conditions, at the same exposure index you used at the event. Then cut the roll in thirds and develop one third at a time until you have the best contrast at that speed. This way you can at least find out how you need to develop your important rolls. The only thing you will not be able to control after the fact is exposure. So the advice then becomes to shoot the film at a lower EI, like 1,000, in order to capture as much shadow detail as possible. It will probably be acceptable at 1,600 too.