@Generic George the thing with multimode fiber is that it suffers from something called modal dispersion. With single mode fiber, the core is very small (9 um, or 0.009 mm), and as such there is only one propagation mode, so the only effects to worry about are loss and chromatic dispersion, which are only a significant factor with long fibers (many km). In multimode fiber, the core is larger (50 um, or 0.05 mm) and as a result there are more ways in which light can propagate down the fiber. Basically, you can think of the light bouncing between the sides of the fiber core, but with different angles. It will still make it to the other end, but depending on the angles, the light can travel a longer or a shorter distance. What happens is you get multiple copies of the signal that effectivley propagate down the fiber at different speeds and then they get mixed together at the receiver, causing intersymbol interference. Bends in the fiber and connectors can also cause modal mixing, where light from one propagation mode ends up in a different propagation mode, so even if you are careful and start out with light in only one mode, you can still end up with light in multiple modes. Anyway, this can be distilled down to a MHz*km factor that basically indicates how many MHz you can send down 1 km of fiber before modal dispersion causes too many bit errors. Higher data rates means shorter bits, which means modal dispersion causes more interference and more bit errors for the same length of fiber. Now, to combat this, the different types of multimode fiber change the design of the core to reduce the number of propagation modes, which means less modal dispersion, which means you can send either more data down the same length of fiber, or the same data down a longer fiber. See
Multi-mode optical fiber - Wikipedia . Looks like if you're going less than 70m, OM3, OM4, and OM5 are all perfectly fine, all the way up to 100G SR4 (although for 100G SR4, you would need an 8 fiber MPO cable instead of a 2 fiber LC cable, although if you pull MPO fiber, you can get breakouts to multiple LC on both ends).
Now, you might wonder, why do we bother with multimode fiber if single mode fiber doesn't have this modal dispersion problem? Not only does multimode fiber cost more, but the length is limited! The answer is transceiver cost. Since the core of a multimode fiber is larger, it requires less precision in the connectors and the optical transceivers in terms of alignment, which can significantly reduce the cost of the transceivers. Multimode fiber is also a bit less sensitive to dust and contamination at the ends of the fiber due to the larger core.