[toast0]

If you're collecting stats anyway, it's not usually too hard to collect a latency metric and process it.

There's room to argue about methodology (ie client vs server latency, where and how timing probes happen), but just pick something and try to measure no more than 10 phases of the requests (timing probes have costs too), and see what happens. After you have a baseline, you can set targets and/or see how releases change your data.