But I'm thinking that when I do upgrade I'll go for a Phison 12 NVMW with TLC chips - which is the "mid point" in performance.

Like:
https://www.amazon.com/Inland-Premium-Internal-Solid-State/dp/B07X74M6PT

Or:
https://www.amazon.com/XPG-SX8200-Gen3x4-3000MB-ASX8200PNP-2TT-C/dp/B07TY2TN64/ref=psdc_1292116011_t1_B07X74M6PT

I'm sure QLC would be fine - but TLC is pretty much the same cost.

Now, I really want a Samsung 970 pro - which is MLC.

One test I saw said "The 970 Pro maintains 2,700 MB/s sequential write performance for 1-hour, again setting a new lab record."

Now, I have no idea why I'd ever write that much data, but it's fun to look at :)