Some other possible changes: in the parallel-building code (from builder.py)
from multiprocessing import Pool, cpu_count
max_cpus = 8 if SAGE_PARALLEL_DOCBUILD else 1
pool = Pool(min(max_cpus, cpu_count()))
perhaps change "else 1" to "else 2"? As it is, building serially (with max_cpus set to 1) is slower than the current system, because in the new system, the manual has to be built twice to resolve cross-references.
We could also change "pool" to just "Pool(cpu_count())" or "Pool(int(1.5 * cpu_count()))" or something like that, eliminating the minimum of 8 and possibly increasing the maximum.
