Hi, I think the biggest resource hogs appear to be compiz, nautilus, evolution calendar, and zeitgeist - of interest it appears that you are running as 'guest' - not as your user - this could have some influence, I may be wrong but you will not be able to stop any processes running whilst being logged on as 'guest'. I would see what happens when you choose to login with 'Zorin Desktop (no effects)' which you choose at point of login by clicking on the 'cog':
You can't really stop Nautilus as that would stop your Window Manager - also evolution bits are embedded in the system for Date and Time function (having researched the issue on various ubuntuesque forums. I believe Wolfman wrote a post on how to remove Zeitgeist.
Hope this helps!