I'm going to install some fibers at work too for AV-networking so I'd like to inquire this information more deeply:
Wikipedia tells me that 100Gbit/s is possible with OM3/4 up to 70/100m. OM5 already exists too and supports even 400Gbit/s. My longest run will not exceed 50m. So I'm planning to install OM4 or OM5 since we will need just 10Gbit/s now and maybe 40Gbit/s in a few years.
Is there anything I'm missing? Is there any good reason to use Singlemode instead?
For 40Gb on single mode (OS1 or OS2) you need just 1 pair of fibers.
For 40Gb on multi mode (OM3) you need 4 pairs of fibers.
For 100Gb on single mode (OS1 or OS2) you need 1 pair.
For 100Gb on multi mode (OM3) you need 10 pairs.
This was the norm with 1 pair of multi mode fibers being able to do 10Gb max. So to get higher speeds, you use multiple pairs on the same transceiver (QSFP+, etc). The 40Gb+ single mode optics accept LC fibers while the multi mode need MPO cables that carry numerous fibers.
There might be transceivers with modulation technology out there that possibly use less multi mode fibers, I am not sure about that. The newer multi mode transceivers also support 25Gb/pair instead of 10Gb/pair.
But in general, multi mode fiber cables get bulky for 40Gb+ applications and the cables come with fixed number of pairs inside them,
so to transition from 40Gb to 100Gb you either need another cable or have to adapt multiple cables to a single connector depends on how many pairs there are in the original cable.
With single mode, you use a duplex LC connector for nearly any speed. Plug and play.
In short, a single pair of duplex LC single mode fiber (2 fibers) can do up to 400Gb.
Whereas you need a 12-pair MPO multi mode cable (industry standard) to do 10-100Gb and a 16-pair MPO multi mode cable to do 400Gb.
With a single mode 12-pair MPO you can theoretically split it to up to 6x 400Gb links.
The difference is distance and density. Also MPO cables tend to be more expensive but so do single mode transceivers.
I have not used 40Gb+ multi mode so take the above with a grain of salt.