memory - Does Windows 7 task manager Performance tab show all RAM and CPU usage for non-admin users?

I'm trying to specify computer upgrades for our CAD computers. IT refuses to give me admin privileges even though I'm the de facto CAD manager. Most of our computers have 8 GB RAM, but I notice mine rarely goes over 6 GB used if I check the "performance" tab of task manager. I know the "Processes" tab is useless for monitoring my overall system needs as it doesn't show administrator tasks. But what about the "Performance" tab? Is it truly showing me overall usage, or just usage for my user's programs? Overall physical memory usage rarely seems to go much over 6 GB (but definitely not over 7 GB), even when I have a couple CAD files open and my typical 20-50 Chrome tabs. I get slowdowns or lag that seem to be from maxing out either RAM or CPU, but Task Manager does not seem to corroborate this. Is it because it is not accounting for administrator tasks?