[Zope] Advice for performance checking/tuning

Hi We are investigating use of Zope for a portal that will have about ~500.000 users. However our test shows that zope is only capable of delivering about 4 request/sec of medium complexity page on dual PIII 833 which seems way too low. We did our tests to straight Zope 2.3.4 (no apache or squid in front of it). Even when told to use 10 thread only 4 were active in top (others were there but were idle) and load average was never over 30%. Where/what should I start investigating ? Where do I find some docs on what makes zope extremely slow (I have found that <dtml-if xxx> where xxx is missing or overly complex authorization schemes can do it, but what else) ? -------------- Hannu