Hi Viswa,
MOB_FIOR_S is for a backend server.
GATEWAY_S is for a front end server.
Quick sizer gives high SAPS for MOB_FIOR_S because client are not SAPGUI. You can just keep the SAPS in mind as a reference. System admin monitors system usage in the production backend and will handle required resources if those are not enough.
Regards,
Masa / SAP Technology RIG