Protection engine for cloud services

HI

I have a customer who wanted to deploy Protection Engine for cloud services but just to use it for URL scan / filtering and not for file scaning

He is an existing user for Scan Engine 5.3 , Currently only 10,000 users

He need the new Protection Engine for Cloud services to be able to support up to 500,000 users.

He need to know how many servers of Scan Engine base on 5million TPS(Transaction per secord) per hour for 500,000 users

Can anyone advise?  I saw the sizing guide is base on file sizes but this customer use it for URL only.

thanks, Lerence