> NetBSD 4.0_RC3 (TANKPAD) #1: Mon Oct 29 17:19:24 CDT 2007

I'd be interested in hearing if a -current kernel worked for you;
IIRC, there were some recent changes involving the latency stuff.

If that does work, you may want to try applying the changes
betwen 1.148 and 1.150 of sys/dev/pci/pccbb.c to your local
source tree to see if it similarly solves your problem.