TB3 But how much speed do I actually need?

[twowheeled]

I really need some advice trying to revive a 2017 27” i7 iMac with a failed Fusion Drive.

The computer has TB3 and usb 3.1 gen 2 per the specs. I have been reading nonstop about tb3 ssd, making my own with an enclosure, speed tests, etc.

None of it makes sense because I don’t know how much speed I actually need to run everything off of an external ssd, macOS and storage. The computer is used mostly for internet browsing, occasional hobby photo editing and 4K video editing. By hobby I mean that I transfer clips, put together short videos, upload to social media, and then delete all clips forever. All my data has never exceeded 1TB. I don’t know what percentage of read/write is simply used up by the OS processes, and how much I need. Realistically I usually transfer around 50gb of video, edit, then delete it. Is my math correct that at 3000MB/s this is finished in 16 seconds? (Way faster than I ever need)



Will I even notice a difference with a usbc ssd?

 

[joevt]

You can replace the internal drives. I replaced the SSD and the HD of my 2013 iMac fusion drive and formatted them so they are not fusion.
Got to macsales.com, click My Upgrades, select your iMac model, and look at the internal drive upgrade options. They have options for the 3.5" HD and the Apple SSD which come with the all the tools needed to get inside the iMac and videos that show the process.
https://eshop.macsales.com/upgrades/imac-retina-5k-27-inch-mid-2017-4.2-ghz/internal-drives

For external drives, TB3 is faster, (at least for sequential reads/writes) but more expensive.
A USB-C enclosure can do 1000 MB/s and is more compatible (you can connect it to a PC or Mac that doesn't have Thunderbolt). Maybe random reads/writes are nearly the same speed? I haven't checked benchmarks recently.