Best way to use a SATA ssd with my laptop for optimum performance

If by “scratch disk” (a Photoshop term) you mean “Media Cache” (AE/PPro, similar idea but different), either way the point of it is to be as close as possible to the speed of RAM.

If the media cache is an internal NVMe SSD then that beats everything else, because many of the current NVMe SSDs can exceed 7000MB/sec when mounted internally. The one you have now might be a little slower, but should be at least 1500MB/sec if it’s old, or at least 2500MB/sec if it’s a newer budget SSD.

If you must use an external media cache volume, here is how their potential top speeds compare to an internally mounted SSD:

Thunderbolt 5: 6000MB/sec+

Thunderbolt 4/USB 4: 3000MB/sec+

USB 3, 10Gb/sec:  1000MB/sec

USB 3, 5Gb/sec:  500MB/sec

Now look at where a SATA SSD ranks within that list.

SATA theoretical top speed is 6Gb/sec (750MB/sec), but in practice, most SATA SSDs might reach 450–550MB/sec. So, if you have a SATA SSD, it is one of the slowest options for a media cache or scratch disk. Only a hard drive is slower!

If you connect the SATA SSD using a 10Gb/sec USB 3 enclosure and cable, the SATA SSD will only be able to use half the potential throughput. So it’s OK to connect a SATA SSD using a 5Gb/sec USB 3 enclosure and cable…but then you still have a slow media cache/scratch disk.

For those reasons, it is better to use the SATA SSD for projects, and use the very fast NVMe SSD for the media cache. But a media cache volume works best if at least 500GB is available, so keep that startup volume cleared out at least that much.

If you find out that the NVMe startup volume doesn’t have enough free space to maintain a good-sized media cache, then you can spend less than $100 on an external NVMe SSD connected using a 10Gb/sec USB 3 enclosure and cable, and assign that for the media cache. That has worked fine for my modest usage of After Effects and Premiere Pro. If your computer has a Thunderbolt 3/4 or USB 4 port, those enclosures are now available for less than $50, so if you put an NVMe SSD into one of those, that would be a much faster external media cache volume than USB 3.

USB 3.0 will probably be too slow for a scratch disk.  Use it for backups or exports (if not in a hurry).

If your NVME is large enough, keep it on the NVME.