I e-mailed Ctein a while back and he said the 50mm Focotar-2 didn't make the cut for his Best Enalrging Lens article(I have 2}. He didn't say why. I have since read that the 50mm F-2 has curvature of field.
I found it to be quite good, although I now use a 50mm Apo-Rodagon, which is really excellent. Although it may well have field curvature, I reckon that stopped down a couple would see it off.
I must admit that 40mm on the V35 is great if you are printing a bit larger, also ties in with the autofocus. I think that Schneider makes a 40mm Apo-Componon...probably very expensive!
It is very expensive, but people rave about the 40mm APO Comp. when used w/the V-35. They say it's much better than the Leitz. I have a 1c, plus several Valoys of diff. vintage.