3dsmax utilize only one core during work in viewport, so CPU will be allways bottleneck. Maximum turbo core frequency is important and your xeons have it 3.6GHz. It is not bad, but when you look at 4 or 6 core intel CPUs on market, they have turbo core frekv. 4.3 - 4.7GHz, which is better for fps.
Anyway, if you set percentage of pointcloud on all corona proxy objects from default 15% to only 1%, you will see another significant improvement in fps. The down side is, that proxy objects does not look attractive in viewport :))