Shooting front yard Halloween displays after dark?

For shooting front yard Halloween displays after dark, do I need to use a faster film speed than ISO 100? I've got Neopan 400 in my fridge; should I use that?

I like to shoot them just after dusk while there is still some ambient daylight remaining. After dark you tend to end up with just the lights floating in an otherwise black frame. Of course, dusk doesn't last very long so it pays to plan ahead and shoot fast.