I can't tell a difference with one texture or even a few. What I'm more concerned about is scenes that have several dozen of them, and I don't have the time to manually resize a whole mess of textures just for an experiment.
I'm more interested in the workings of it anyway, and I can't seem to find an answer as to the technicalities of how a graphics card deals with textures on a 3D object. I'm hoping someone can either confirm or refute what I asked.

But anyway, resizing textures shouldn't be my job, if I buy a texture pack, not to mention that resizing a .jpg texture and resaving it as such would result in a slight loss of quality, while saving it as bmp or png would result in any mat-pose files not finding the textures.

Besides, if I'm right about this, even if the additional processing power is minimal, I would think the people at DAZ would know about it, and know better. It might be minimal and negligible with a few textures, but what about with a hundred?