Test your disk drives with the USB 3.0 connection and see what performance they supply. Not all USB controller live up to theoretical transfer rates. If you use something like CrystalDiskMark you get very optimistic readings because hard disk drives slow down as they fill up. and that test really is only great for SSD drives A good test that demonstrates this best is HDTune. Here is a 1TB 7200 rpm drive with a SATA III interface that you can use for reference (I do not have a USB 3 enclosure to test) but USB 3 should not affect transfer rates
Just show you great USB 3 transfer rates from a device like the Samsung T3 portable SSD here is a test on my system:
Apple does not make a Thunderbolt 3 to FireWire800 adapter.
- Use the USB3 connector (as mentioned above); however, as I'm sure that you're aware you will not be able to daisy-chain other FireWire drives.
- Use the Thunderbolt 3 to Thunderbolt 2/1 adapter and then use the Thunderbolt 2/1 to FireWire800 adapter. If your FireWire drive has more than one FW port, you can still daisy chain other FireWire devices.
- Use the OtherWorld Computing Thunderbolt 3 Dock (when is ships, available for pre-rode now): The New OWC Thunderbolt 3 Dock - Pre-Order Today. If your FireWire drive has more than one FW port, you can still daisy chain other FireWire devices.