Production is NEVER the same at dev, test, staging, etc.

But it is a real world starting point number for performance testing, when the app goes live. Maybe you have a 24 core xeon to play with in dev. Maybe you get a 1/2 core in prod. You'll never know until it is too late. The hardware guys and sysadmins and dbas willl NEVER give you the real numbers that would cause them to be the "responsible" party for the app.

They did not write it.

So, all "live" numbers are variable, out of your control, unless you have this exact test. Call it your "ready for production final qa"(must run in production environment for the real app to run test), and therefor it MUST be in that environment.

Then don't forget your peak usage time concurrent test. Can't trust the starting number, gotta see what's happening in the real world. Do the test as often as you can as long as you are not causing any degradation in the rest of the world. How often you run depends on how much headroom the app/os leaves you, and then you still have to leave a comfy level for spikes in the apps.