In heavy tasks like stacking 100 images, or creating HDRs, or exporting several hundred images for time lapse, and combining those hundreds of images as a layer and exporting them as a time-lapse video, etc, how much does the write speed of SSD matter? A PCIe is 5x faster than an NVMe which is 5x faster than a SATA3 SSD, theoretically. How much of this translates into real life image export times?
Look at your CPU and RAM usage during a simple export (not a bunch of processor-heavy stuff like noise reduction, moire, clarity). If either CPU or RAM are maxed out they're your bottleneck. Given that 90ish% (or # of cores x 90% for a Mac) is effectively maxed out.
Only if both are some distance from maximum should you consider drive speed as a bottleneck.
My Hackintosh is 4 x 3.75ghz. A 7200-rpm drive isn't enough to make the CPU a bottleneck, but a bargain SSD is. No gain from a good Samsung SATA SSD nor an NVMe. 16gb of RAM is plenty if I don't have a bunch of other things going on--Lightroom doesn't seem to grab crazy amounts of RAM even if it's there.
Once a program has to page to a storage device, performance drops. An SSD is less of a performance drop than a conventional hard disk and NVMe is potentially less of a performance drop than SATA3.
The ideal approach is usually more RAM because it reduces the amount of data flowing through the bottle neck that is the storage subsystem. DRAM is not just faster byte for byte, the data it contains can be cached at L1, L2, and L3. Accessing anything that has been paged to disk almost certainly means cache misses at all those levels. Multicore CPU's can also access RAM in parallel and graphics operations are amenable to parallelization (that's why GPU's have all those cores).
These days, 32GB or 64GB of DRAM is not exotic or expensive. A small 'fast' SSD will probably cost as much or more.