Though people on WP doing admin, if you have 6 people, are unlikely to be doing things every second - most of it is writing stuff, looking at things, so even if they were doing a click every second that's still 6 requests per second that for even completely non-cached dynamic stuff is completely irrelevant.
The only way to make WP "fast" is to make it nearly completely static.
Get a half dozen people working admin area and your server will cry.