Experimentally we've loaded 2.6.3 kernel packages onto coronelli, one of the squid caches. If it dies completely, we can swap the IP back to browne to take over. If coronelli reboots, it should revert to the 2.4.x it had before (hopefully).
If things seem positive and more performant, we'll upgrade the others in turn.
I'm using the test packages for Red Hat 9 from: http://people.redhat.com/arjanv/2.5/
-- brion vibber (brion @ pobox.com)