Hi,i don't know if it helps, but i have uptimes of several weeks with my VAX, and have high loads (rebuilding X, pkgsrc-packages, etc) and never experienced an unresponsive System.
My NetBSD version is at the moment 5.1-RC4, but i hadn't any problems with any version newer than 5.1-RC1. But i'm using the M2-scheduler... Lukas