I think he should make an educated decision based on his compiler's performance and how it handles the non-standard behavior.
The difference in performance is going to be completely negligible until he has an absolutely massive project - and even then the compile times will probably be dominated by 3rd party headers, not his own.
As for standard vs non-standard behaviour, it takes less time to discover that than it did for any of us to type out an answer here. If only one of the 2 options is available, the question becomes irrelevant, and if both options are available, the answer is uninteresting - just pick one.