Yeah. If you need something to dig deep, you need to try Fable (optionally in /goal mode).

For performance testing, I wrote isolated testbeds that try to impair the system in realistic ways (latency/jitter/bandwidth limit on logical WAN hops when load testing), and Fable is happy to send a bunch of agents at it and iterate until it gets the results it's looking for.

I think that if you are used to Sonnet medium or something, this will surprise you, but models like Fable and Sol on high/xhigh will really dig deep until they meet your goal. (I mostly use this for bug hunting and not perf, but ... I think it can do perf if you set it up right.)