Exactly! For me, it seems everytime I go above 74 pounds of draw weight my grouping with fix blades opens up beyond that which is acceptable. This is due to planing effects caused by higher speeds. It is tremendously significant beyond forty yards. Please keep in mind, not all of us hunt from ground blind when we travel to Africa. I grew up spot and stalking in open country. This is still my preferred style of hunting. A fix blade will fail to open if it cannot hit the target.
Mechanicals came about because the speed of the bows jumped drastically in the 90's and it became hard to get fixed blade BH's to fly right, hence mechanicals.