Sporgon, is there a large difference between primes and zooms at this f stop?
In the context of common focal lengths for landscape, Canon have rewritten the rule book with the 24-70/2.8II and the 16-35/4.
However looking at other common FF standard or wide zooms such as the 24-105, the 24-70 IS, 17-40, 16-35/2.8II, a good quality prime is better edge of frame to mid, and in the four corners at f8. Centre can be identical. I am bearing in mind that 'landscape' normally means trying to define and resolve small detail that is a relatively long way away.
At f11 I cannot, for instance, see any difference between my 24-105 @ 50mm and my EF 50/1.4 at the same aperture, even at 100% on a studio tripod.
When shooting subject that are closer to the camera I find at f8 the differences are much slimmer, but landscape is a different ball game. This is why until recently the large format cameras reigned supreme in this sphere, and even now you are better with a larger format for serious work due to the greater magnification of the subject.