Now to answer your actual question, 100gph per 1" of waterfall is recommended. So for 72" wide waterfall you would be looking for 7,200 gph. I use two sequence 4400gph pumps for my waterfall. It is 48" wide. I haven't used any of W.Lim's pumps, but I think one of the Wave II series pumps would work for you
Wave II Series - W. Lim Corporation - 2007