This is the answer I got on the Adobe Forums:
“Running over 8 background processes does not show a significant gain based on testing a while ago on [our beastly machine]. In some cases it was a bit slower with >8 background CPUs for Render Multiple Frames Simultaneously multiprocessing. Given the small frame sizes they are rendering and the performance degradation running too many cores, I would think their proposal would be overkill unless they are also using other memory hungry apps on it.
I think they’d get better performance for their dollar with a 24 or 32GB 8-12 core machine, setting the background CPU allocation to 3GB. Spend the extra bucks on processor speed + bus speed with fast drives.”