Speakers don't have RMS watts. If these speakers are intended to be run off of the OEM BMW amp, all they have to do is handle that power. Any additional power handling is irrelevant. If the speaker does have more power handling, it has ZERO to do with sound quality - doesn't make it sound better.
Manual, you may want to learn more about how to evaluate speakers.
There are areas, like off-axis response, resonant frequency and "Q" characteristics, and distortion components, which can make clear differences in how a speaker sounds.
BSW doesn't usually share these details either, but they COULD...
