Pretty cool to hear about your process - I've been thinking about this space a lot so have some context about pain points here.
I've found that building a benchmark is something that's easy-ish on the surface level, but has many layers of technical complexity the deep you go down the rabbit hole.
For example, a tangent on grading. Do you use test passing and/or LLM graders? If you're using an LLM, it's fairly easy to spin up a basic LLM grader. But - is that grader calibrated? Is it biasing towards same-model agents? How many results do you need to be above the noise floor? What is it even measuring, and is that aligned with what you care about? Does it have the right information to make those judgement calls?
I'm super curious how what you've been using this workflow for? Also happy to answer any questions / discuss further!