I installed the 188.8.131.52 upgrade and try to generate 300 frames with 8.5.4 and the latest plug-in (Mac Pro 4,1 with 12 Gb RAM and OSX 10.10.5).
With the latest early build formZ took few minutes, now with 184.108.40.206 plug-in took 1 hour and 40 minutes (with base animation disable).
I installed the 220.127.116.11 plug-in because early build worked great but with same 300 animation frames some random frames (9 of 300) had mxs trees scatter moved different for the rest of frames.
I tryed to generate manuallt only the problematic frames but the scatter mxs are moved again. (i don't to disabled base animation with the early build).
I don't know if with the 18.104.22.168 plug-in and base animation disabled the generation frames long time is aspected;
The project is too big to send you but if the animation will the same frames problem i consider to send you formZ project with all textures and dipendencies.