Migrating to Postgresql and new hardware

Hi,

We are in the process of moving a web based application from a MySql to Postgresql database.
Our main reason for moving to Postgresql is problems with MySql (MyISAM) table locking.
We will buy a new set of servers to run the Postgresql databases.

The current setup is five Dell PowerEdge 2950 with 2 * XEON E5410, 4GB RAM. PERC 5/I 256MB NV Cache, 4 * 10K Disks (3 in RAID 5 + 1 spare).

One server is used for shared data.
Four servers are used for sharded data. A user in the system only has data in one of the shards.
There is another server to which all data is replicated but I'll leave that one out of this discussion.
These are dedicated database servers. There are more or less no stored procedures. The shared database size is about 20GB and each shard database is about 40GB (total of 20 + 40 * 4 = 180GB). I would expect the size will grow 10%-15% this year. Server load might increase with 15%-30% this year. This setup is disk I/O bound. The overwhelming majority of sql statements are fast (typically single row selects, updates, inserts and deletes on primary key) but there are some slow long running (10min) queries.

As new server we are thinking of PowerEdge R510, 1 * Xeon X5650, 24Gb RAM, H700 512MB NV Cache.
Dell has offered two alternative SSDs:
Samsung model SS805 (100GB Solid State Disk SATA 2.5").
(http://www.plianttechnology.com/lightning_lb.php)
Pliant model LB 150S (149GB Solid State Drive SAS 3Gbps 2.5"). (http://www.samsung.com/global/business/semiconductor/products/SSD/Products_Enterprise_SSD.html)

Both are SLC drives. The price of the Pliant is about 2,3 times the price of the Samsung (does it have twice the performance?).

One alternative is 5 servers (1 shared and 4 shards) with 5 Samsung drives (4 in RAID 10 + 1 spare).
Another alternative would be 3 servers (1 shared and 2 shards) with 5 Pliant drives (4 in RAID 10 + 1 spare). This would be slightly more expensive than the first alternative but would be easier to upgrade with two new shard servers when it's needed.

Anyone have experience using the Samsung or the Pliant SSD? Any information about degraded performance over time?
Any comments on the setups? How would an alternative with 15K disks (6 RAID 10 + 1 spare, or even 10 RAID10 + 1 spare) compare?
How would these alternatives compare in I/O performance compared to the old setup?
Anyone care to guess how the two alternatives would compare in performance running Postgresql?
How would the hardware usage of Postgresql compare to MySqls?

Regards
/Lars