lowering impact of checkpoints

hi,
our system is handling between 600 and 2000 transactions per second. all
of them are very small, very fast. typical query runs in under 1ms.
yes - sometimes we get queries that take longer than then should get.
simple check shows that we have a very visible pattern of
every-5-minutes peak.
in the minute that there is checkpoint - we get usually 15-20 times more
queries "over 500 ms" than in other minutes.

we are using 8.2.4 (upgrade will be soon), with these settings:
# select name, setting, unit from pg_settings where name ~* 'bgwriter|wal|checkpoint';
name | setting | unit
-----------------------+-----------+--------
bgwriter_all_maxpages | 5 |
bgwriter_all_percent | 0.333 | [null]
bgwriter_delay | 200 | ms
bgwriter_lru_maxpages | 5 |
bgwriter_lru_percent | 1 | [null]
checkpoint_segments | 32 |
checkpoint_timeout | 300 | s
checkpoint_warning | 30 | s
wal_buffers | 128 | 8kB
wal_sync_method | fdatasync | [null]
(10 rows)

is there anything i can change to make it "smoother"?

depesz

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