Folks,
I am cautiously optimistic that I may have improved the situation. The server load is still high, but through a number of changes I think I've made it manageable.
For those who care, I think the core of the problem was that with recent upgrade made our PHP accelerator fail to load however it didn't log an error, it just aborted. That meant we were running without an accelerator, but I didn't realize it. I've now sync'd the versions and the accelerator is back online.
I've also put in a firewall ban for most of Asiapac, but I intend to lift that if the server load remains tolerable.
Thanks for your patience, and fingers crossed, this will see us through to the new hardware.
Cheers
Mike