We know that 1000BASE-LX transceivers can be used over multimode fiber, and should be able to reach distances of 550 m in addition to the usual 10 km over single mode fiber. 10GBASE-LR transceivers have the same 10 km rated distance over single mode, but I've seen no mention of using them over multimode, even for short distances.
What happens in practice with 10GBASE-LR over multimode, can it work at all? Is the difference in MMF performance between 1000BASE-LX and 10GBASE-LR just about the speed, or is there some other factor involved?
Then there is 10GBASE-LRM, which should work over 220 m of multimode fiber, even ancient OM1 fibers. But it's rated for only 300 m over single mode fiber. What does LRM do differently from LR to work better over multimode but so much worse over single mode?