> If it's faster, they can benchmark before and after

That goes bad very fast. I've worked with someone who tried winning arguments with one-line microbenchmarks; They even tried to convince me that I should always use undefined over null in JS since one is faster than the other (forgot which).

> Introduce them to the concept of static single assignment form

I failed with this as well; some coders don't trust the compiler/runtime at all. I had people tell me that garbage collectors don't deal with cyclic dependencies or that "simple comparisons" (<, >, ==) are faster than "compound comparisons" (<=, >=).