@trawglodyte asked me about external USB4 speeds and I thought I'd share this with you.
This might be of use to somebody and I hope it's easier to find in this subforum.
I got myself a new PC and an external USB4 SSD enclosure.
my tldr experience:
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check the effective possible speed to save money on the SSD itself
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cables matter
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an actively cooled enclosure is helpful if you expect longer/bigger transfers
Speed calculations
USB4 (first version) supports 40 Gbps, i.e. 5,000 MB/s
The protocol overhead is said to be about 15%. Subtract from theoretical maximum: 5,000 MB/s - 750 MB/s = 4,250 MB/s.
We can expect up to ~ 4,250 MB/s then.
So no need to go shopping for the latest Gen5 SSD. A solid Gen4 SSD might suffice, even a fast Gen3 SSD might be all you need for your use case.
The case itself
I bought an actively cooled NVMe SSD metal case. It has a small fan spinning.
Yes, it is noisy when under sustained load. But I can keep max speeds over longer periods this way (e.g. when transferring large backup files to the external drive).
The surprise: cables really matter.
My case came with an included USB4 cable. How nice!
It got me to about 1940 MB/s read speeds. Which is nice in itself, but...
...with a "good" cable, under otherwise identical conditions, got me 3850 MB/s. That's nearly doubled! 
And here are my 2 screenshots of the benchmark with included cable and "certified USB4 40 Gbps for EUR 20" cable:
- usb_benchmark_included_cable.png (155.68 KiB) Viewed 621 times
- usb_benchmark_included_cable.png (155.68 KiB) Viewed 621 times
Hope this helps you!
Any questions, let me know
