I'll be curious to hear where you land on this question, dogberry. I've been wrestling with the same question, and just purchased a mono cartridge to begin my investigations. I'll be happy to report findings if anyone is interested.
I purchased a zyx mono cartridge. zyx options weren't necessarily on my radar but I got a good deal on the cartridge bundled with a tonearm. The zyx carts are all 1.0 mil, spherical stylus. I'm good with that as an option for now. I have plenty of old mono classical records that I suspect will be best served with the 1.0 mil option. For modern mono reissues, I'll try the mono cartridge and my stereo cartridge to see which I prefer.
None of my phono preamps have a mono switch. And the comparison between the mono and stereo carts won't exactly be scientific - they will be on slightly different tonearms and the stereo cart is from a different maker altogether. Still. Fun is about to happen.