The Shield was way ahead of its time back in 2015, and shouldn’t have performance problems. ?

PC speaker bitrate is fine at 11025 kHz. It sounds weird in 44.1 CD quality anyway.
I was being a bit unclear, too: for general midi / soundfonts, you’ll only need to set mixer rate to either 44100 or 48000, as there isn’t a bitrate option for that.
Only if you’re using MT32 emulation, you’ll have to adjust the MT32 bitrate as well. MT32 also has a tendency to slow down emulation. Other than Soundblaster/Aflib, sound won’t skip, but cause kind of a rubberband effect instead. This will only happen if you deliberately overload your cpu though. ?