As for std::algorithms not being zero-cost. I have seen cases were std::foreach was noticably faster or much slower. I have seen it in benchmarks and it seems largely to be a quality of implementation issue.

Good implementations can cheat and use knowledge my code shouldn't have about parts of the underlying system and bad ones do extra useless crap.

Benchmarking and profiling seem to be the only real way to gain confidence in your results reliably.