[]AllenAyres said:
As a stop-gap measure, you might try turning off zlib compression - it can make a significant server load difference on a busy site. [/]
Our problems are resolved, our forums have been flying. Part of it was self-inflicted, part was IMHO 6.4.1 sensitivity to a properly tuned my.cnf.
I will make a full new post on what we did. I have been waiting a few days just to make sure our problems are all resolved.