The best presentation I've seen about CPU performance related to pipelining, branch prediction, and speculative execution was Chandler Carruth's "Going Nowhere Faster" presentation at CppCon 2017 [0]. I do recommend watching the whole presentation, but if you watch nothing else then just watch the 5 minutes or so from the linked timestamp.

[0]: https://youtu.be/2EWejmkKlxs?t=2511

It also contains a wonderfully prescient question asked right at the end of the talk: "... the processor gonna speculate, doing some loads out of the bounds of the array, how does it work in the hardware that it doesn't crash?"

Left unanswered at the time. I believe Spectre was known but not publicly disclosed at this time.