What kind of screws should be used to attach metal stud runners at the top of a metal framed demising wall to wood framing members at the flooring joists above?

Use the one's in the strong tie asile in Home depot. You know the metal lumber helper things.

Coarse thread screws. Something like drywall screws or wood screws.

You can see a picture when you click on the first link in the document. Strong-Drive® SD Screw for Structural Connectors

Closer to a drywall screw.

I've used screws that were not from simpson that had a square drive head and a course thread.