Apologies regular readers, it is most unlikely this is going to be of any interest or even use to you, but I just wanted to jot this down for posteriority.
If you are lucky enough to have access to a Photron Fastcam and have run into performance issues, make sure you enable Jumbo Frames on your network interface and in the Fastcam Viewer software (see e.g. here).
However, this recently stopped working for me, and it turned out that although I was setting the Jumbo Frames / Jumbo Packet settings in the Windows control panel as instructed, this was not actually set in the network adapter itself. Only after resorting to some command line action I managed the setting to be actual used, and things worked again with the usual performance.
Here’s what I used (thanks to this blog post for spelling it out):
To see what interfaces you have on your computer, type
netsh interface ipv4 show subinterfaces
To change the MTU, type
netsh interface ipv4 set subinterface "Local Area Connection" mtu=nnnn store=persistent
Local Area Connection is the name of the network connection on your computer, from the list obtained above, and nnnn is the desired value for MTU.
Reboot after making the change.
An MTU size of 9014 did it for me, and it worked straight away without rebooting.