postgres on a beowulf? (AMD)opteron?

Has anyone run postgres on a beowulf system?

I'm shopping for a new server. One candidate would be a
quad opteron (64-bit AMD "hammer") machine. Another approach might
be a beowulf of single or dual opterons. I imagine the beowulf
would be a bit cheaper, and much more expandable, but what about
the shared memory used by the postgres backends? I gather that
postgres uses shared memory to coordinate (locks?) between backends?

I have a smallish DB (pgdump|bzip2 -> 10MB), with ~45 users logged in
using local X(python/gtk) postgres client apps.

Will the much slower shared memory access between beowulf nodes be
a performance bottleneck?

[Next question is: has anyone used postgres on an opteron at all??]

-- George
--
I cannot think why the whole bed of the ocean is
not one solid mass of oysters, so prolific they seem. Ah,
I am wandering! Strange how the brain controls the brain!
-- Sherlock Holmes in "The Dying Detective"