Agreed on J12's being wonky lens-to-lens. So many of them have been badly worked on (including two that I owned in m39). On the other hand the one that I had for Kneb/Contax mount was just stellar.
The yashica 35cc I had suffered from the same problem as my yashica 124-g: Radial bokeh. Looking at the prints with their weird swirly bokeh made me motion sick. Then again I hurled during Blair Witch Project and can't read in the car. YMMV.