We're launching a library called Loam. Loam allows GDAL to be used in client-side code in a web application. Loam wraps a version of GDAL compiled to WebAssembly and makes the GDAL API and utilities available to Javascript running from within a web browser.

k6.io provides a flexible base for load testing with a convenient scripting language, and the quickstart docs will get you pretty far, but testing with a session of TMS requests had some unique challenges.