Here is a little recording. I thought it was very interesting when I compared the output of my Sega Game Gear (heard from 0:00 to 1:23) to the output of my Sega Master System II (from 1:24 to 2:47). The exact same data was used to generate these two recordings. Both have been normalised, however the GG was about 30 dB quieter than the SMS.
The output from the GG was via the headphone jack - I'm guessing it has some broken caps that need replacing, hence the lack of volume and the very dull nature of the sound. The output from the SMS was directly from the VDP chip via a line out I added (since the SMS2 only has an RF modulator for output).
Of course, this is only my SMS and GG, so please keep that in mind when listening.
Download here (1.9 MB)