EIM Merge Slow for Contacts and Accounts

Hi,

We are running EIM Merge process for Contacts and Accounts. However, its performance is very slow. It takes 6-7 hours to process 17k records.

We have modified our Ifb with reference to Index hints and Using Synonyms. Log Transaction is TRUE and Set Based Logging is FALSE.

I have few questions:

1. Are there any other approach to be followed in order to improve performance of Merge Process.

2. Is it mandatory to keep Log Transaction TRUE and Set Based Logging FALSE for EIM Merge Process

3. What is optimum batch size for EIM Merge process. We are using 5000 records per batch