The first step is not to use technical measures like throughput or response time, but to use business units (like ATM account balance checks or withdrawals), so you can forecast capacity according to business plans.
In modern web apps, that's served by issuing a transaction id to user actions, and tracing that through all the systems and sub-systems required to service that transaction. That's your data plane.
Unfortunately, the next step of applying queuing theory to your software model is almost moot in a multi-core, multi-machine world with GPU's on a modern memory bus, because the model cannot be both abstract and accurate.
But the real problem is cultural: IT is willing to set targets for measures it can own and manipulate, but it's much, much less willing to commit to business unit measures that senior management can see clearly. Indeed, one of the best ways to understand how IT fits into the organization is to ask what's being measured.