It doesn't seem that laughable to me to want faster JSON parsing on a Chromebook, given how heavily JSON is used to communicate between webservers and client-side Javascript.

"Faster" meaning faster than Chromebooks do now; 2.2 GB/s may simply be unachievable hardware-wise with these cheap processors. They're kinda slow, so any speed increase would be welcome.

There is no real penalty for switching between SSE and AVX2, unless you do it wrong. What are you referring to specifically?

Are you talking about state transition penalties that can occur if you forget a vzeroupper? That's the only thing I'm aware of which kind of matches that.