Typical link speeds between COs

[Jean-Francois Mezei <jfmezei_nanog () vaxination ca>]

What are the typical speeds used on fibre links between COs in North
American and elsewhere ?

I realise that there are special cases, such as Shaw using WDM to reach
400gigabits/sec in a link in Western Canada. But what are the most
common speeds ?

Is WDM in common use to multiplex multiple 10gbps, 40gbps links ? Or is
that used mostly for intercity trunks and intra-city trunks tend to not
bother with WDM because of ample supply of fibre ?

Do telcos typically quickly upgrade fibre strands to newer speeds, or
are there still many strands handling only 100mbps or 1gbps between COs
because telcos never got around to upgrading legacy equipment/services
(such as ATM etc) ?

Also in terms of costing WDM, would one typically have a card that has
the multiple colours in the card and outputs a single multi-colour
signal or would one typically have separate cards for each colour and
then use a WDM "filter" to combine/separate colours onto the single strand ?