Question about hosting and server grade

Hi. I have a questionf or people who run high traffic websites.

We are considering a new dedicated server host for a set of 25
domains, about 5 of which are very high traffic (80 million clicks a
day each). A lot of this is VIEW content, but there may be a million
or so INSERTs and UPDATEs.

I am told that the biggest speed boost and performance comes from
memory and fast hard disk. So I'm looking for at least a 16GB RAM and
SCSI 10k 300GB hard disks.

We will use CentOS 5 with Apache 2. I am also told that PHP etc is
okay, but Postgresql (the database) is the one that hogs resources
after a while. So for the database server I need a high end server.

My question: What's the high end recommendation? Is the following
config of 4 x quadcore Dunnington Intels with 4 disks on RAID 10 be
good enough for the above sites? Can I run a database on this config
of servers for my kind of traffic, or do I need a separate one for PG?
I suppose the traffic will grow large quite quickly so the 300GB may
be low, but that we can add as we go along.

Thanks for any thoughts!

--------
Quad Processor Hex Core Intel 7450 - 2.40GHz (Dunnington) - 6 x 9MB
(L2) 12MB (L3) cache

Second Processor
Hex Core Intel 7450 - 2.40GHz (Dunnington) - 6 x 9MB (L2) 12MB (L3)

Third Processor
Hex Core Intel 7450 - 2.40GHz (Dunnington) - 6 x 9MB (L2) 12MB (L3) cache

Fourth Processor
Hex Core Intel 7450 - 2.40GHz (Dunnington) - 6 x 9MB (L2) 12MB (L3) cache

16 GB FB-DIMM Registered 533/667

1000 Mbps public uplink
1000 Mbps private uplink

Disk Controller RAID 10

HD1: 300GB SA-SCSI 10K RPM
HD2: 300GB SA-SCSI 10K RPM
HD3: 300GB SA-SCSI 10K RPM
HD4: 300GB SA-SCSI 10K RPM

CentOS 5 (32 bit)