Fortunately, we are not going to rely on any photographic gear to pass IIHS collision testing . . .
I have tested all my Pentax manual focus prime lenses - all bought used, using Kodak Techpan shot at ISO25 and processed in Technidol and they are all excellent performers. Of course if they were factory fresh they would be even better. In any case, they will not be the weak link in your system particularly if you don't use equally resolving film, used impeccable technique and shot a scene in ideal conditions.
Actually, I have also started all my other original equipment manual focus prime lenses - Canon, Konica, Minolta, Nikon, Olympus and Yashica, and they all appear to be equally excellent performers to the point that they are unlikely to be the weak link in a system.
However, I support capitalism and I say spend your money as you see fit!