<p>I have the Canon FD 50mm f1.8 S.C. and 50mm f1.4 S.S.C. lenses and had the 50mm f1.2L lens, and I do find the 50mm f1.4 S.S.C. to be slightly better than the f1.8 version, but not drastically, and found the 50mm f1.2L to be slightly better than the f1.4 version, but not better enough to justify the cost difference. And all three lenses were either bought brand new, or overhauled by Ken in California, so they were all to factory spec.</p>
<p>I think if you pick up a 50mm f1.4 S.S.C. or New FD version, you should be good to go in the 50mm focal length range.</p>