Using some 2048 materials, means minutes between Ghosted and any kind of textured preview. For a small file, with a few 2048s, it’s 1:29 to switch. About one second to switch back to Ghosted.
Rhino using a disk cache for mappings is likely part of the problem. It would seem that there will not be acceptable performance with large materials until the mappings are done in memory.
Also, texture caches and mappings sometimes become corrupted, necessitating file reloading. When it get’s slow, it gets worse.
Either/Both: AMD 3900x, GTX 1080 and Intel i9-11950H, RTX Quadro A3000