gin index creation performance problems

I'm looking for a bit more guidance on gin index creation.

The process:
- vaccum analyze.
- start a transaction that:
- drop the triggers to update a tsvector
- drop the index on the tsvector
- fill several tables
- update the tsvector in a table with ~800K records
- recreate the gin index
- commit

To have a rough idea of the data involved:
- 800K record
- tsvector formed from concatenation of 6 fields
- total length of concatenated fields ~ 200 chars *
- average N of lexemes in tsvector 10 *
[*] guessed

2xXeon HT 3.2GHz, 4Gb RAM, SCSI RAID5

Index creation takes more than 1h.

maintenance_work_mem is still untouched. What would be a good value
to start from?
Anything else to do to improve performances?

--
Ivan Sergio Borgonovo
http://www.webthatworks.it