We usually go around 8/20 and the crowds are manageable. Probably around a 4 during the week and more like a 6 on the weekend (1-10 scale). Weekends are still busy at the end of august.
We previously went the beginning of may and the end of August crowds Aren't as quiet as beginning of may
I went near the end of August a few years ago. Crowds are down but the heat is oppressive. Humidity will best you down. Drinks tons and tons of water or you will get sick. Personally, I will never go during that time again.