Someone posted a video here recently taken with their 920 of a club event- they said it was taken very near the speaker stacks with levels around 100dB, the audio was fine.
There was also a video taken at an Everclear concert with similarly good sound quality. It seems the 920's mics aren't overwhelmed by higher dB levels like some other phones, with none of the awful distortion/limiting that often makes such vids unuseable. Apparently there are 2 mics in the 920 in addition to the talk mic, so stereo recording could be enabled as a firmware update- here's hoping!
Can't really comment on the playback capability of the speakers in the 920 regarding playback of bass-heavy video. All I will say is that phone speakers and bass shouldn't be mentioned in the same sentence- as regardless of any processing tricks, phone speakers will never be able to reproduce real bass frequencies. Plug it in to something that can.
Apologies if you know all of this stuff already!
edit- I should have said that if your video is distortion-free (which with the 920 it is likely to be), the playback should be fine too. I've maxed out the speakers on mine to ful volume and it copes admirably.