I have a real PAL NES hooked up to a modern TV with an AV-to-HDMI adapter (yeah, I'm working on finding a CRT). I bought an EverDrive cartridge for it because I'm a poor person who cannot afford to actually collect original video games cartridges, even though I would obviously vastly prefer to be able to do so, just for the feeling of switching cartridges and whatnot.
Skipping a long story about the hardships of finding non-garbage ROM collections, I placed the PAL version of Super Mario Bros., among others, on the EverDrive and ran it as the first game.
The music that played seemed to go too fast. I immediately suspected that either this was a mislabeled NTSC ROM, or the EverDrive was somehow messing with it. However, all the other games seemed to run at the correct speed.
I then spent many hours trying numerous different ROMs of the game from different sources, and trying to hunt down gameplay footage on YouTube of a real PAL NES playing the PAL version of the game, but the latter proved seemingly impossible and none of the ROMs seemed to play the game at the "correct" speed.
But since it's about 30 years since I actually got my NES for my birthday with the game, and both are sadly long gone, I cannot rely on my memory for this. It might very well be that the game does play with faster music on the PAL version, and my memories have just been muddled up over the years from hearing the song played on NTSC NES consoles, or NTSC emulators/ROMs. In fact, this is the most probable explanation IMO.
Nevertheless, Nintendo did go through the trouble to "optimize" the game for PAL after they had made the original NTSC-J and NTSC-USA versions, so why did they (apparently) have the music still play at a noticeably faster pace?
It's important to emphasize that I'm not talking about running an NTSC game on a PAL console or a PAL game on an NTSC console, so that's not the reason it sounds faster. This is a PAL game on a PAL console, yet still has faster music than the NTSC version on an NTSC console.