No, I had the newest rb 50 (given the small price difference, it's never made sense to me to invest in older rb lenses). And I don't think it was an issue of a bad copy, the rb 50 and the 50 uld are quite different designs. The rb 50 is not a low dispersion lens.
By the way, when I had the rb 50, I also compared it to the 50 on my mamiya 6. Not good, not good. The rb 50 wasn't even approximately in the same league. Mind you, the rangefinder 50 might well be among the very best lenses ever made. The 50 uld, on the other hand, seems almost as good, especially considering that it covers 6x7.
So, begging to differ but the rb 50 is not very good in my opinion. Of course I am happy if you are happy, and certainly we all have different needs. But when somebody asks for advice, I'll call it as I see (or saw) it. I have written many positive things about other rb lenses, but the 50, nah.