Optimized my.cnf for high-end and busy server
If you're running at that load on that hardware, you really should get some experts in to do this for you. Pythian and Percona are 2 consultancy/support organisations that I can think of: I have no link to either of them BTW.

Each install and load has different tweaks needed. The "huge" cases for my.cnf files I've seen are what you'd use a few years ago or on your mobile phone nowadays...

The default settings are amazingly low so if you've never changed them then there is your problem.

Edit: Have you already hacked your my.cnf? https://drupal.stackexchange.com/questions/12085/default-to-myisam-instead-of-innodb-in-drupal-7