Apache + PHP + Postgres Interaction

Hello.

I have a subject setup and a few questions.

The first one is this. PHP establishes a connection to the Postgres
database through pg_pconnect(). Then it
runs some query, then the script returns, leaving the persistent
connection hanging. But the trouble
is that in this case any query takes significantly more time to execute
than in the case of one PHP script
running the same query with different parameters for N times. How can I
achieve the same performance in the first
case? Persistent connections help but not enough - the queries are still
10 times slower than they would be on
the 2nd time.

The second one is that the machine with this setup is dual core Xeon
2.8ghz. I've read somewhere about
the switching context problem and bad postgres performance. What are the
effects? What are the symptoms?
And what will be the performance gain if I change the machine to equal
Athlon?

Thank you in advance.