netbsd-4 vs -current web server performance

[Jeff Rizzo <riz%tastylime.net@localhost>]

Our website is run by a (small) pool of webservers running NetBSD -
until recently, both running netbsd-4 (4.0_BETA2, actually) behind a
load balancer (f5, if it matters)

We're in the process of expanding the pool, so I replaced one of the
machines with a shiny new one running -current as of week or so ago,
since -current has so much better multithreaded performance.  Things
seemed to be going fairly well since the update last Friday, but the
machine running -current seemed to be having some trouble today (the
monitor we have running kept taking it out of the pool, which means it
wasn't responding properly on port 80).

Looking at both machines, the one running 4 was at its normal load -
between 4 and 5 - but the machine running -current had a load of about
12, and many of the httpd processes were showing as 'parked' in top, and
there were no idle cpus. Restarting apache on the affected machine seems
to have brought things back to normal - both machines have a load just
under 3, and all CPUs (8 per box) have ~80% idle.

Both machines are running apache 2.2 compiled with the worker MPM,
though slightly different versions (2.2.6 on the netbsd-4 machine, 2.2.9
on the -current machine) and PHP (5.2.4 vs 5.2.6).    If/when this
happens again, what sort of information can I gather to help figure out
what's going on?  

Thanks,
+j