Carl's right - I didn't consider the effects of head travel.
BTW PG 7.0 has a transaction log, too, that's fsynch'd with every transaction that does a write). PG 7.0 also flushes every modified data page and fsynch's the table files after every transaction that changes data.
PG 7.1 only flushes the WAL and fsynch's it at transaction end - it doesn't flush data to disk nor does it fsynch the data file. This is why inserts and updates run so much faster on PG 7.1 (data is flushed and table files fsynch'd every so often - by default about every five minutes - in PG 7.1). If there's a crash, the WAL is used to restore the data that didn't get written to the table files.
So putting the WAL on an ext2 disk would get you the greatest performance gain, I should think. That seems to fit with what you're telling us.
