[Brightcolours]

To claim the difference in IQ is huge between 135 format and cropped digital MF is silly. People who say that either:

• Use a lesser lens on 135 format, and claim the difference is because of sensor related things
  
• Are easily impressed by the oversharpened/false detail - fake sharpness look of the MF results due to the lack of AA-filter
  
• Don't make actual comparisons but put more thought into the MF shots because of the limitations of the gear, ending up being impressed by their own efforts instead of difference in sensor size.
  

If you do make real equivalent settings comparisons, and use good lenses for both, it is pretty difficult to distinguish the results from eachother. Besides different aspect ratios and the lack of AA-filter for the MF combo, of course.

Same as that it is pretty difficult to distinguish results from APS-C with FF, with equivalent settings.

In your case, going from 1D-X to MF, my guess is that you get taken in by the higher resolution sensor and the fake detail and oversharpenedness that you get from the lack of AA-filter, and that the size of the sensor has little to do with it.