For many years my favourite camera was my Rolleicord V. This has now been joined by a Rolleiflex and a Yashica-mat LM, both from my father's collection.
I should really try them both out to see how they compare but I doubt that I will be able to tell any difference between them or with the Rolleicord.
I tend to use f8 more than any other stop so I won't see any differences in the lenses wide open which is where most of the reported differences are.
As far as build quality is concerned - I haven't taken a Yashica apart but externally, it seems o.k. However, judging by the sound of the shutter and the feel of the wind on, I can tell that it doesn't quite have the manufacturing precision of the Rolleicord or Rolleiflex. I'm sure that when they were new, this was reflected in the price. Otherwise I doubt that many Yashicas would have been sold.