Performance advice for a new low(er)-power server

Hi,

I am evaluating hardware for a new PostgreSQL server. For reasons
concerning power consumption and available space it should not have
more than 4 disks (in a 1U case), if possible. Now, I am not sure what
disks to use and how to layout them to get the best performance.

The cheaper option would be to buy 15k Seagate SAS disks with a 3ware
9750SA (battery backed) controller. Does it matter whether to use a
4-disk RAID10 or 2x 2-disk RAID1 (system+pg_xlog , pg_data) setup? Am
I right that both would be faster than just using a single 2-disk
RAID1 for everything?

A higher end option would be to use 2x 64G Intel X-25E SSD's with a
LSI MegaRAID 9261 controller for pg_data and/or pg_xlog and 2x SAS
disks for the rest. Unfortunately, these SSD are the only ones offered
by our supplier and they don't use a supercapacitor, AFAIK. Therefore
I would have to disable the write cache on the SSD's somehow and just
use the cache on the controller only. Does anyone know if this will
work or even uses such a setup?

Furthermore, the LSI MegaRAID 9261 offers CacheCade which uses SSD
disks a as secondary tier of cache for the SAS disks. Would this
feature make sense for a PostgreSQL server, performance wise?

Thank you for any hints and inputs.

Regards,

Tom.