We take our claims if correctness very seriously. The behavior you're describing, depending on exactly what you're doing, is likely an allowed serializable history, which is the isolation level we claim to support. See [0] for a deeper dive on the subject. Either way, you should show us what you found (if you haven't already).
As for your performance analysis, do share your results and methodology. We published an in-depth, reproducible comparison with YugaByte here [1] in addition to publishing our TPCC-100k numbers[2]. If you're seeing performance that doesn't line up with the above, let us know.
[0]: https://www.cockroachlabs.com/blog/consistency-model/
[1]: https://www.cockroachlabs.com/blog/unpacking-competitive-ben...