I'm biased towards high quality zooms and always thought that cropping the next widest prime lens to capture your subject would negate the resolution advantage the prime lens might have.
If you can't move closer, which is often the case, the resolution of your sensor is utilized better with a lens zoomed in, this usually is not discussed in these debates.
There are lots of comparisons that can be made at Photozone, comparing the resolution of prime lenses with zooms of a longer focal length. Dividing the longer focal length of any particular zoom by the shorter focal length of a particular prime gives one the effective crop factor, which in turn allows one to calculate the resulting resolution of the image from the prime lens that has been cropped to the same FoV as the image from the longer focal length
I have only a couple of Nikkor lenses, both zooms. I've recently ordered the AF-S 85/1.8G because it seems remarkably sharp and good value. It's certainly much sharper at F4 than my Nikkor 24-120/F4 is at 85mm and F4, according to Photozone's tests on the D3X. It's also sharper at F8, but to a lesser degree.
Out of curiosity I wondered how it would compare with the 24-120 at its weakest focal length of 120mm, shooting from the same position with both lenses.
The crop factor is 120/85 = 1.4. The centre resolution of the 85mm prime at F8 is 3693 LW/PH. Dividing that figure by 1.4 gives us a resolution of 2638 LW/PH.
Now, according to Photozone, the resolution of the Nikkor 24-120 at 120mm and F8 is 3385 LW/PH. I'm quite sure there would be a very noticeable difference in practice between these two resolutions of 2638 and 3385.
In other words, if I happen to have the Nikkor 85/1.8G attached to my camera but need a 120mm focal length because I can't move closer, for whatever reason, I should get noticeably better results in the centre of the image by switching lenses and using the 24-120 zoom at 120mm.
However, the borders are another matter. If one crops the image from the prime lens, then the Photozone results for the borders and extreme borders don't apply. The figures will be higher because the borders will be closer to the centre. It looks as though in this example, comparing an excellent prime with a medium quality zoom of longer focal length, the prime might still retain equal or even better sharpness at the borders.
When the lenses are compared at F4, 85mm cropped to the 120mm FoV, it appears that the 85mm prime should actually still be sharper at the borders, though still not quite as sharp in the centre, ie, 2766 for the cropped image compared to 3025 for the zoom at 120mm.
When I receive my 85/1.8G prime, I might try to confirm this with some tests, just to get a handle on the practical significance of any differences.