Mark:
I adjusted the height based on your response. The highest point is 50 inches up and the lowest is 31 inches. I dropped all 10 inches lower.
Ultimately, you can determine where you want it to be. There are two places where the tracks cross over one another. At those points the closest one is 7 inches up which is extra room and you aren't going to run tall equipment. 6 would be fine for 99% of O scale stuff anyway. Think about it...