As far as I'm aware, no. System requirements are for versions of QlikView Server (Extranet is a different license, not a different product).
However, it is likely that
- you have different apps published, but the same sizing principles apply than to a "normal" QlikView Server
- and that extranet users use a different method of authentication than internal users, although this is more a configuration topic.
EDIT: Worth mentioning in addition that, unless it has been changed recently
- QES only uses Session CALs (or even Usage, but not Named or Document, again, a configuration topic)
- If Workbench is used instead of the built-in Ajax client, then yes, software requirements such as .NET versions will apply, depending on the custom development