PostgreSQL and Xeon MP

Hello,

We are experiencing performances problem with a quad Xeon MP and
PostgreSQL 7.4 for a year now. Our context switch rate is not so high
but the load of the server is blocked to 4 even on very high load and
we have 60% cpu idle even in this case. Our database fits in RAM and
we don't have any IO problem. I saw this post from Tom Lane
http://archives.postgresql.org/pgsql-performance/2004-04/msg00249.php
and several other references to problem with Xeon MP and I suspect our
problems are related to this.
We tried to put our production load on a dual standard Xeon on monday
and it performs far better with the same configuration parameters.

I know that work has been done by Tom for PostgreSQL 8.1 on
multiprocessor support but I didn't find any information on if it
solves the problem with Xeon MP or not.

My question is should we expect a resolution of our problem by
switching to 8.1 or will we still have problems and should we consider
a hardware change? We will try to upgrade next tuesday so we will have
the real answer soon but if anyone has any experience or information
on this, he will be very welcome.

Thanks for your help.

--
Guillaume