The Exercism problems have proven to be very effective at measuring an LLM's ability to modify existing code. I receive a lot of feedback that the aider benchmarks correlate strongly with people's "vibes" on model coding skill. I agree. The scores have felt quite aligned with my hands-on experience coding with most of the top models over the last 18+ months.
To be clear, the purpose of the benchmark is to help me quantitatively assess and improve aider and make it more effective. But it's also turned out to be a great way to measure the coding skill of LLMs.