Outlook Synchronisation very slow after adding hotfix

Hello,
due to the incorrect transfer of German special characters like 'ä', 'ö' 'ß' I programmed the hotfix given in Article 970764 on Partner Source. After that, special characters are transferred correctly.
However, when I use Filtering in the Outlook Synch. User Setup, e.g. Salesperson Code in Contacts, the synchronisation slows down heavyly. In fact, transfering ALL contacts from Navision to Outlook goes faster.
Has anyone here allready faced this problem?
Perhaps I should add, that I use the full synchronisation, as I have to establish Navision Contacts in Outlook for a customer once. Unfortunately, it is seemly not possible to get all Navision Contacts to the customers Outlook account at once (over 4500 contacts), so I have transfer them in intervalls, determined by setting filters.
When using my Outlook account at the network in my firm, transfering such an amount of data is not a problem.

With kind regards