Are you looking for real time metrics or historical? If you want real time, you can browse to Monitor > Performance, like you mentioned or you can get data from the CLI using the "stats" command. I've written a blog about some of the cool data you can get from the stats command:
Using the CLI might be your best bet to get information in the space requirements you're looking for.
If you're looking for historical data, InfoSight is invaluable. I hope this helps!
Cli would be hard to put on a monitor for people to easily read and translate to how the system is going. Having a monitor user on the web interface would be good, however it seems there is an inactivity timeout of 30 minutes. I would want this monitoring user to be logged in long time and just have access to the Monitor>performance page. Is this possible?