Exam 1Y0-402 topic 1 question 102 discussion

Scenario: During an assessment of a Citrix Infrastructure, a Citrix Architect finds that there are four active Sites. Each Site has one NetScaler SDX pair and two
StoreFront servers in a server group to allow access for internal and external users. Users have to use different URLs when they access resources from different
Sites. Single-factor authentication is used for both internal and external access. NetScaler appliances are placed in the DMZ with the appropriate firewall ports configured to allow Citrix traffic. Many of the internal users connect using corporate-owned laptops and some external users also connect using personal devices.
Management is planning to create one more Site and has asked the architect to perform scalability testing and advise how many NetScaler appliances are needed for the new Site.
What is the primary determining factor that the architect can use to help identify the appropriate NetScaler platform in this scenario?