[Zope] help performance

Hi! I've an old machine with zope 2.6 with an application based on ZClass. Now, updating 4000 record takes ages (more than an hour...), basically it is a propertysheet update + recatalog of every object of 4000. Can I have significative performance upgrade changing something in the code base? Some ZCatalog "slow" bug in 2.6 I could patch you know of? :) TIA