Good Sound Quality From 10 Inch Records?

Nope.

My experience is the material used on those 10" is different from the vinyl from the mid-50s onwards used on LPs.

It seems much more brittle and easier to scratch, hence the poorer sound on average.

Do you mean 78rpm records? Which speed are you playing them at -- 33 or 45?

No, I'm not referring to 78s. Thankfully, I know enough to not to play a 78 RPM record with my Shelter 501 cartridge, as I believe it would risk damaging my cartridge and/or the record. I'm talking about, for instance 10 inch records by folks such as Duke Ellington, Edith Piaf, and Lena Horne. In fact, they even say 33 1/3 RPM on the cover. Some famous records, including Peggy Lee's Black Coffee originally came out in 10 inch format (I don't have that one). Another one, I think, is June Christy's Something Cool (don't have that one either). I think Blue Note released some records in the 10 inch 33 rpm format as well.

Have you tried a mono cartridge? I use an Ortofon Mono SPU with a .1 mil conical stylus--it seems to work pretty well.

I will try to get a mono cartridge at some point, as you suggest. First, I guess, I'll get a turntable that can accept two arms, as I mostly listen to stereo. But I'll have to save up some funds for that. Other than reducing noise, what other advantage have you found using a mono cartridge with such vintage records?