LDAP administration limits in Active Directory

LDAP Limits In Active Directory From MS.

How to view and set LDAP policy in Active Directory by using Ntdsutil.exe

Active Directory Performance Testing Tool

Here are AD performance testing tool from MS.

Active Directory Performance Testing Tool

Active Directory Performance for 64-bit Versions of Windows Server 2003

Troubleshooting Active Directory performance problems

Here is some good articles for troubleshooting Active Directory performance problems

SolutionBase: Troubleshooting Active Directory performance problems

SolutionBase: Discover Active Directory performance problems with Performance Monitor