> Well, Serhiy Storchaka asked for a microbenchmark. 
> For an optimization, it's a reasonable request no?

As noted above, it not reasonable for a C-API that isn't used internally because there is no reasonable way to measure the effect without writing a C extension.

FWIW, I look at assembly to see direct evidence for the effect of a change.  It makes it easy to see how many memory accesses happen on a given path.

If you're going to be in the optimization business, I really wish you would read some of the basics in the field so that each and every technique doesn't have to be re-proved to you each time it used.  Here's a short-list I put together for those who were interested : https://dl.dropboxusercontent.com/u/3967849/sftalk/_build/html/misc.html#optimization-resources