Generally, lenses are sharpest about 2-3 stops down from wide open,
if clinical sharpness is what you're looking for. But nobody looks at emotional work in terms of lines per millimeter, and strong photography is often strongly emotional.
Real world impressions of sharpness often increase as you stop the lens down, however. I shot a bunch of images at f/16-22 yesterday, knowing that although they wouldn't resolve the absolute detail I'd get at f/5.6-f/8, the impression of sharpness would be greater because I was shooting three dimensional subjects. If the near and far edge of a rock are both sharp, it feels sharper than if only one side is sharp, even if the sharp side is 100 lines/mm. It worked most excellently, largely because I was using the same tripod I use for my 8"x10" camera. These D70s are very capable machines when we do our part.
The world is like that.
My 50 f/1.8 works very well with the Nikon "plus" lenses which screw into the filter threads. I have carried these "plus" lenses in a 6" stack of screwed-together filters since the '70s, for "macro" work, among other things. It sure beats carrying around another (expensive, heavy-after-12-hours) lens, although my old Micro Nikkors were among my all-time favorites. If I had a Micro Nikkor D series lens, I'd carry it, but if you do your job, nobody will care what lens you used, and only perception-deficients will ask.
On a D70, the 50mm's function like 75mm's on 35mm film cameras, nice for
moderate portraits, and very fast. That means that you must be VERY careful where you put the precise focusing plane, and I don't find autofocus to be anywhere near precise enough. You want focus on the prominent
eyeball, not the bridge of the subject's nose. And a D70 requires extraordinary care to place the focus where you want it.
Shoot sharp, y'all,
Joe