for answering questions like this some more information are needed.
The numbers you are talking about are the database size (right?) and not the size of your qlikview application loaded in memory.
How many users are working at the same time with an application.
The best way to handle this is to ask your local qlikview account manager. He/She will have access to "QlikView Expert Services" if needed.
This is depending on the document size and the memory uses per document.
Also it depends on the number of users.
More memory you have less problems you'll have !
You can at lease check the memory used during the reload of each application. Because sometimes we forget to take this temporary amount of memory which is needed during the reload.
You Qlikview sales partner should help you to size your server.