Hard to imagine the CV 58/1.4 needing repair... concerning sample variation, no idea because it is anyway difficult to find them.
From what I saw, the 58/1.4G is nearly free from purple haze wide open, which is probably due to its better correction of spherical aberration (and yes, it is sharper wide open). So I'd recommend the old CV as a backup in case the Nikkor needs repair. At smaller apertures, the CV has no weakness, and its bokeh is very nice, maybe not quite Nikkor 58/1.4G level, but better than most other 50mm Nikkors. Not to mention the excellent (and useful) resistance to flare.
