> But do the millions you spend a year on compute cost more or less than the millions you would spend a year in labor finding the increasingly rare breed of C++ developers who can optimize things for instruction or cycle count?

That's a very valid question but in the case of Facebook they already have them so why not use them for that?

I mean yeah, they made their choice -- use HHVM and it likely served them very well. I am just pointing out that in their case sourcing extra (or even any at all) C++ devs is a non-issue because they already have plenty.

Fully agreed with your memory latency remark.