I think you need to re-read that toms review.
You wrote that IOPS are what people "feel"
Here's what the article states regarding IOPS
"The real performance increase comes from reading random data. The SM951 (AHCI) spec sheet claims up to 90,000 random read IOPS. That's less than
the 850 Pro, which tops out at up to 100,000 IOPS. Although we managed to pull more random read IOPS from the AHCI drive, it
couldn't come close to the SM951-NVMe's claimed 300,000 random read IOPS."
You also wrote that regardless of benchmark results, there "was no difference" between the drives.
Here's what the article states regarding usable difference
"This is why we rarely mix SATA-attached drives into our PCIe-based comparisons.
The performance gap is very wide, like comparing hard drives to SSDs. When solid-state storage first emerged, readers wanted to see us compare the technology to the fastest mechanical disks. We are still in a place where enthusiasts need to see the difference with SSDs, even though
the gap is massive. Next-generation isn't just a marketing term for the companies manufacturing these parts.
Comparing the SM951-NVMe to the 850 Pro, we see the equivalent of a two-generation increase at low queue depths. Most users spend 80% of their time reading data and around 20% writing it. Those requests are typically random in nature. Given both stipulations,
you're looking at a very large performance boost over the 850 Pro."
Given these quotes, it's difficult to read them and conclude they support your point that there is no, or even a marginal, difference in performance between SATA and NVMe; rather the differences are described as analogous to the difference between rotational drives and SSDs.
Buying one for half price on the used market as
iamMacPerson points out, however, does net a sizable enough discount to make a compelling argument for the viability of an older clamshell MacBook Pro.