By default, SAN switches are able to determine/negotiate the link speed for FC channels.
For example, if you purchase a SAN switch supports 2,8,16Gb, and comes with a 2,4,16Gb XFP. At the other side, The HBA card supports 16Gb link speed too. Connecting them together, they will auto negotiate to the highest speed, 16Gb FC speed.
However, if you noticed your FC link speed is not the one you expected(see 8Gb for example), after checking other components, make sure you don't forget Fibre Cable.
Here is the cable specification metric. The OM? value usually can be found on the cable.
Hope it helps