I have the same cards in 2 PCs, work well at 40Gb/s. AfaIk, you will need a FDR capable switch to enable 56Gb/s, SX6036F
will do it.
I bought a couple of Mellanox MC2207310 cables cheap on ebay. I also bought some optical cables only, no transceivers,
50/125µm multimode fiber ( NO 62,5/125µm ! ). From another source on ebay I bought the transceivers for US $ 2.25 ea.
This source has thousands of these transceivers with cut off fibers ( cannibalized ), all I bought work flawlessly,
2 transceivers + 1 optical cable = MC2207310
BR speedy