That's for sure. Shooting at 4000 on a 1.6 crop sensor is unthinkable to me. I don't think one could ever get such images past a review panel at a stock agency. In fact, for professional work where the licensee is inspecting every submission at 100%, I don't think ISO 4000 images from any 1.6 sensor would ever get through QC.
Does the OP submit images to a stock agency? It wasn't specified if they were shooting for themselves or for a stock agency.
I would say maybe we need to know the end game for the shots taken to know if we are giving good advice here.
On the other hand, many stock agencies don't even bother to inspect anymore, SS and IS are pretty much accepting anything, nowadays, sadly.