Okay so contact your 35mm prints so no one can possibly perceive any grain regardless of how close they go.
Originally Posted by Noble
Or realize that it's up to the viewer ultimately and if they want to diminish the experience by staring at any grain then that's they're problem. It does not obviate printing at some nebulous "no visible grain" enlargement size.
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.