a very good true mono cartridge will outperform ANY stereo cartridge on mono pressings. i have three very expensive stereo cartridges with better arms and cables than my 2 mono carts. yet playing mono pressings the mono's are better even though they have a list price 20% of the stereo cartridges.
here is a link to the Ortofon website about mono cartridges. scroll down past the mono cartridge models and it gets into the reason mono's sound better on mono pressings. and they are right.
Experience authentic sound with Ortofon's mono cartridges, crafted for optimal playback of mono records.
www.ortofon.com
the ideal mono cartridge does vary whether the pressing is an early wide groove (1.0 mil) or later stereo cutter head (0.7 mil) mono (mid 60's and after).