The answer is highly scanner-dependent and image-dependent, and also on the effect you're trying to schieve. I have used drum scanners, Imacon/Hasselblad Flextight scanners, and flatbed scanners.
Drum scanners are the most problematical with silver negs, although they do better with color, both chromes and negs. The collimated read beam does similar things to the image as a condenser head in an enlarger. Too big an aperture, and you miss detail. Too small an aperture, and you get an effect known as "grain aliasing".
With the Imacon scanners, I used to scan at the maximum resolution that I wanted for the output file, and sort out the grain in post. The Imacon wasn't sharp enough to suffer from grain aliasing.
With flatbed scanners, you should realize that many of them "achieve" the highest resolutions by interpolation. You can do that better in post. If you have such a scanner, I'd start at the highest native resolution, and see if the grain looks mushy. If it does, then you're probably not gonna get aliasing, and you can scan at that resolution, providing you want files that big.
Eliminating all the visible grain at scan time is, IMHO, a really bad idea. There are things you can do in post that will damage the images much less than just lowering the scan resolution.