I am building this ECS in my spare time. Complete description with examples you can find in readme on github.
https://github.com/helioscout/moecs
If you want the highest performance, it's best not to use any ECS. I love ECS because it allows you to systematize and separate/parallelize logic/data, move each part of the game into its own system, customize its operation, and generalize logic for entities with different components. As for speed, it will vary on different computers. You can play around with main.odin, and see the benchmarks (I use this code for testing). I'd be interested in seeing your results.
My tests show this:
With 7 components, 3 systems, 1 million entities, 6 archetypes, world progress 100 times takes 56 milliseconds (at each iteration: 1 system adding component to 100 entities and despawning one entity and 2 others getting 6 components for each entity).
I also built simple space game as a demo.
