All of my 94's are pre-64 but I have handled post-64 versions. Side by side I think the bluing looks better on the older guns then the newer. The newer ones are more black and less polished then the older ones.
I have a 1950 version that has never been fired and is nearly ANIB. It is exceptionally nice. If I had the need and a 1951 popped up I would buy it, but right now I am sort of full up of shooter 30/30's.
Look at it pragmatically, why NOT get the pre-64 if the opportunity presents itself?
10mm and 357sig, the best things to come along since the 38 super!