Maximum reasonable free space map

Hi Everyone,

Just wondering what the maximum reasonable free space map setting should be?  I'm receiving the
following advice from vacuum:

INFO:  free space map contains 170803 pages in 117 relations
DETAIL:  A total of 185000 page slots are in use (including overhead).
733008 page slots are required to track all free space.
Current limits are:  185000 page slots, 5000 relations, using 1623 KB.
NOTICE:  number of page slots needed (733008) exceeds max_fsm_pages (185000)
HINT:  Consider increasing the configuration parameter "max_fsm_pages" to a value over 733008.

I thought 185K was pretty high, is going to 700K+ reasonable?  I've got 16GB of ram and am running
very high volume 100GB+ DBs.

Cheers
Phil