Client-side rendering is gaining in popularity which presents new challenges for measuring and optimizing end-to-end performance on the web. BrowserLab provides a controlled, consistent environment for collecting timing metrics which is capable of detecting regressions as small as 20ms. This talk will cover techniques that we apply to handle highly dynamic content, isolate server variance from client-side performance, deal with non-deterministic code, and enable engineers to understand performance implications of their changes.