* 2x25G throughput is higher than 40G,
* 25G latency is lower than 40G,
* you can use 25G ports as 10G ports, and
* you can use DACs to connect 4x25G <=> 100G
That last point is particularly relevant given the existence of switches like the Mikrotik CRS504, providing 4x100G ports on 25W.
if you run all older mellanox gear the cx3 can do the kinda nonstandard 56gbe as well
I am still on 1gbe... I guess I don't transfer anything bigger than a few GiB time to time.
* 2x25G throughput is higher than 40G,
* 25G latency is lower than 40G,
* you can use 25G ports as 10G ports, and
* you can use DACs to connect 4x25G <=> 100G
That last point is particularly relevant given the existence of switches like the Mikrotik CRS504, providing 4x100G ports on 25W.