stress testing and performance monitoring

Hi,

I am migrating a database to postgresql, with a data schema change.
I'd need to do some stress testing (on the db design I have, not
a general test a la TPC). I'm just starting to look at this,
 and would appreciate any advice on:
- existing tools (I've seen http://ltp.sourceforge.net/dotshowto.php,
http://dbmonster.kernelpanic.pl/index.html,http://jakarta.apache.org/jmeter/
but still need to test them)
- links and docs to read on db stress testing

I guess the most significant measure is the time needed to complete operations
(read, insert, delete), but I guess other measurements are advisable.
I also wonder what I should measure server side. I've read the docs
on pg_stat* (http://www.postgresql.org/docs/7.4/static/monitoring-stats.html#MONITORING-STATS-VIEWS-TABLE),
 but I don't know how I should interpret results, and what I should really pay attention to.

I also plan to monitor the postgres server during the test phase an production phase,
but I'm not sure what I should keep an eye on exactly.

I hope my request is not too general, and that someone on this list has done some
stress testing and can give good advices.

Thanks.

Raph