There's very little speed difference in real-world use because the bottleneck is 4k speeds. And both SATA and PCIe SSDs have almost the same 4k speeds. The extra bandwidth of PCIe does not give you any advantage for 4k speeds which are down around 30 MB/s.

Say to load up a game the computer needs to read 1 GB of contiguous files (sequential read) and 1 GB of small files.

The SATA drive has 500 MB/s sequential speeds, 30 MB/s 4k speeds.
The PCIe drive has 2 GB/s sequential speeds, 30 MB/s 4k speeds.

- SATA drive takes (1 GB / 500 MB/s) = 2 sec to read the sequential data, 1 GB / 30 MB/s = 34.1 sec to read the 4k data. Total time is 36.1 sec.

- PCIe drive takes (1 GB / 2 GB/s) = 0.5 sec to read the sequential data, 1 GB / 30 MB/s = 34.1 sec to read the 4k data. Total time is 34.6 sec.

99.9% of people will not be able to tell the difference between 34.6 sec and 36.1 sec without a stopwatch.

This is why I keep telling people to ignore the sequential speeds and instead concentrate on the 4k speeds and IOPS. In the above two examples, 94% - 98% of the drive's time is spent on the 4k reads. So a SATA drive with slightly faster at 4k read/writes will actually be faster in real use than a PCIe drive with much faster sequential speeds. e.g. If the SATA drive has 35 MB/s 4k speeds.

- (1 GB / 500 MB/s) = 2 sec for sequential data. 1 GB / 35 MB/s = 29.3 sec to read the 4k data. Total time = 31.3 sec, which beats the PCIe SSD with slower 4k speeds.

If the drive with the best 4k/IOPS is a PCIe drive, great! But if it's a SATA drive, I would get that SATA drive.