Catalog on external SSD - Read/Write Speed Performance

Hi, I’m thinking about to buy a SSD enclosure (40Gbps) with a 2-4TB M.2 PCIe Gen3 NVMe SSD (up to 3500MB/s) and connect it via Thunderbot / USB 4 to my MacBook Pro M1.

My RAW images are stored all on a 18TB Harddisk.

I guess it will be ca. the half speed of Apple's internal soldered SSD.

Unless I need to render new previews from the RAW images, I only access the catalog, right? How is the performance to read and write these catalogs, which contains the rendered previews compared to the internal SSD?

P.S. I remember when working with Lightroom and other DAM software, I  disconnected the harddrive with the original images and forced the software to  diplay only the rendered previews without reading and rendering the previews again.