we have reviewed our magento performance. And it is OK, within limits now 😉
There are 2 exceptions
But! changing and editing settings (going to system, config) is just plain slow: viewing, and changing is almost impossible.
Also adding a product to the cart takes 10 secs.
Any advice on a special index I can set?
Add APC caching to the Magento backend
Sounds like mysql is struggling – try running mysqltuner.pl for some hints