I wish someone would eliminate that word "significant" from the dictionary. Mono cartridges are the better choice for mono recordings since the cartridge only has to respond to horizontal movements in a mono record groove. You'll usually find the noise floor to be lower with a mono cartridge even when your amplifier has a "mono" switch. MF did a column on mono cartridges not too long ago and discussed the advantages of using a dedicated mono cartridge along with a suggestion for how to wire a stereo cartridge to appear as a "virtual" mono output without the vertical response meant for a 45/45 stereo groove. MF isn't in the Stereophile on line archives so you'll have to search through the back issues to find the article. Possibly someone here can direct you to the correct issue to make the task a bit easier.

No many monos out there, but I've seen reviews of a mono Grado Sonata that praised it highly.

Art Dudley did a whole review of nothing but monos- that should get you going!

AD Mono Cartridges Overview