Cluster and vacuum performance

I have a few questions about cluster and vacuum.
We have a table that is 56 GB in size and after a purge based on dates 16GB
was made available as reported below.
PWFPM_DEV=# vacuum full verbose analyze forecastelement;
INFO: vacuuming "public.forecastelement"
INFO: "forecastelement": found 93351479 removable, 219177133 nonremovable
row versions in 6621806 pages
DETAIL: 0 dead row versions cannot be removed yet.
Nonremovable row versions range from 156 to 192 bytes long.
There were 611201 unused item pointers.
Total free space (including removable row versions) is 16296891960 bytes.
1974172 pages are or will become empty, including 26 at the end of the
table.
1990268 pages containing 15794855436 free bytes are potential move
destinations.
CPU 467.29s/48.52u sec elapsed 4121.69 sec.

How can you improve the performance of cluster?
1. BY increasing sort_mem?
2. Does increasing vacuum_mem help?
3. Does checkpoint_segments improve it?

Dan