If you're writing the same code, almost certainly not. The only way there would be would be if the compiler either can't optimize something as well because the

If you're writing the same code, almost certainly not. The only way there would be would be if the compiler either can't optimize something as well because the lang changes requirements (this seems unlikely), or if they have bugs or inefficiencies because they haven't spent much time on the new standard. If you're using new stuff from the new standard, they could be slower or faster or undecidable, really depends.