A question regarding the caching of VDB's from a smoke simulation.

Currently see well over 160 million vel voxels when I load some cached vdbs from a sim.

That combined with 5 substeps necessary in my simulation is choking my Threadripper, simulation times are simply too long.

Since all I really need are density voxels (and optionally temperature or heat) for rendering, does it make sense to delete these vel voxels just before caching?

If you want motion blur on the smoke, you will want that velocity field as well.

The resolution definitely doesn't have to be as high as the density though. You can reduce the velocity VDB with the VDB Resample node, set it to “Using Voxel Scale Only” and increase the voxel scale to a multitude (Voxel Scale>1).

before converting to VDB you can use Volume Compress to compress the values and also mask out or set all volumes to 0 outside of density
also changing bit depth to 16bit on VDB (using Primitive SOP) can help