For some reason, Mr. Rorslett did not review the 50/1.4 AI(S) in his legacy site :
http://www.naturfotograf.com/index2.html.
However he reviewed the 50/1.4 SC.
I have seen some reviews stating that the 50/1.4 was sharper than the 50/1.8 at f/2.0, i.e. coming to opposite conclusions. However, from experience, it is darn difficult to come to any conclusion when comparing decent lenses. The slightest misfocus, or uncorrected focus shift, will lead to different stories.
It is striking to see how strong opinions (starting with my own) may be, where careful tests will rather raise doubts.
Ultimately, I can only support your last piece of advice (own several and choose by the whim of the moment).