[jraph]

Actually, the only two comparable / equivalent options exposed in this page related to this discussion, ul > * + * vs li:not(:first-child), are 50.8ms vs 40.9ms (respectively) for 10 page loads. The browser is not named, so I would guess Chrome. I'm not convinced the difference is not proven significant, we need more data points than that to know for sure, but it seems insignificant. So yes, readability should be the determining factor here.

Other browsers might see different results, especially Firefox which has a very fast / efficient CSS engine.

ps: a difference of 43 ms for one page load would be huge indeed. By comparison, a frame in a 30 fps video is 33 ms.