Connection problem under extreme load.

We have been doing some load testing with postgresql, and we have been
getting the following error when libpq attempts to connect to the
backend.  This only happens occasionally and, as I said under extreme
load (e.g. load average 30+ on a single processor Sun).

connectDBStart() -- connect() failed: Connection refused
Is the postmaster running at 'localhost' and accepting connections on
Unix socket '6700'?

Has anyone seen this before or know what could be happening?  One theory
that we have is that the connection request timed out because the server
was under such heavy load that it couldn't respond to the request.  Is
this possible?

Thank you,
Jeff Collins