On NES games the music plays way too fast, and on SNES games, there are minor issues with the sound.
I can't speak to the SNES issues, but I believe both lr-fceumm and lr-nestopia need to be aware that a game is PAL before they will play at the correct speed. If I remember correctly, lr-nestopia achieves this by checking the NstDatabase.xml file in your BIOS folder and lr-fceumm checks for "PAL" to be included in the file name. Outside of that, you can also force PAL from the core options in the RetroArch menu as well.