I did feel my post was a bit unneeded when I added my edit :)

   My point about the  30% was that you mentioned that he got in rust and attributed it to essentially, better algorithms in the rust lib he used.  Once he knew that then its hard to say that rust is 'faster' but the point is valid and I accept that he gained performance by using the rust library.

   My other point was that the speed of his code probably didn't matter at the time. If it was a problem in the past he probably would have taken the time to profile and gain some more speed.  Sure you cant gain speed that can't be had but as you pointed out, it wasn't a language issue, it was an implementation of the library issue.

   He could have arbitrarily used a different program that used a good library and the results reversed.

   I also agree that most devs are not working down at that level of optimisation so the default libraries can help but at the same time it mostly doesnt matter if something takes 30% longer if that overall time is not a problem.   If you are working on something where the speed really matters and you are trying to shave off milliseconds then you have to be that developer that can work C or Rust at that level.