How to setup disk spindles for best performance

I'm currently trying to find out what the best configuration is for
our new database server. It will server a database of about 80 GB and
growing fast. The new machine has plenty of memory (64GB) and 16 SAS
disks, of wich two are already in use as a mirror for the OS.

The rest can be used for PostgreSQL. So that makes a total of 14 15k.5
SAS diks. There is obviously a lot to interesting reading to be found,
most of them stating that the transaction log should be put onto a
separate disk spindle. You can also do this with the indexes. Since
they will be updated a lot, I guess that might be a good idea. But
what no-one states, is what performance these spindle should have in
comparison to the data spindle? If I create a raid 10 of 6 disks for
the data, 4 disk raid 10 for the log, and 4 disk raid 10 for the
indexes, will this yield best performance? Or is it sufficient to just
have a simple mirror for the log and/or indexes...? I have not found
any information about these figures, and I guess it should be possible
to give some pointers on how these different setup might affect
performance?

So I hope someone has already tested this and can give some tips...

Kind regards,

Christiaan