if its a stress test, i wouldnt do it on live relays, but a periodic ping of what a client would do in separate geolocations x1 is useful
My smoke test with Playwright will be timed, and I could run it in parallel across a set of relays, on an hourly basis, and then post pretty trend diagrams on https://status.gitcitadel.com .
Discussion
I said smoke test, not stress test. It's just one happy path e2e in a headless browser.
i call it "smokeping" because there was a cool monitoring tool called that, written in perl back in the day.. it was my #1 fav thing for seeing status of the end to end service and it's trends over time.
i do this and publish as nip66 latency events and to influxdb for querying. very useful, not on the same network as the relay (geo distributed). It connects and does a simple REQ, records total latency. 
for a stress test of relay software itself you usually have to be running it on the same hardware configuration. maybe we can work together on benchmarking somehow though anyway, everybody loves benchmarks