What Steve and Phil said. What I've done to show my argument is give them this type of scenario.:
If there are 20 users each with the Launcher + avg of 4 screens opens, that is 5 pvxwin32 processes / user running on server. Then multiplied by 20 users that is 100 pvxwin32.exe sessions. If each one takes 48 MB on avg (which is embellished of course), then that is 4.8 GB of RAM needed. Not to mention what the App Server needs itself and CS ODBC Driver (up to 1 GB if heavily used). So there you've exceeded 6 GB already. And what if there is more than 100 sessions --> then more RAM is needed.
I'm usually recommending between 8 - 16 GB of RAM for Advanced depending on number of users and other apps (SQL Server, SQL apps, non-SQL apps). If SQL and/or other apps involved then 16 - 32 GB depending on other factors. I also always ask the question of future growth a year from now in terms of Sage new users, new apps on the Sage server, etc and if that's foreseeable then add more RAM.
Doug I would be more concerned with asking how many processor cores are allocated.