I would not worry too much, as soon as it is handholded quality cannot be challenged/scratched anyway.
at least the 6x6 2.8/50 gives round bokeh rings...
There was a whitepaper on the Markins Ballhead website, actually comparing heads with and w/o Mirror Lockup MLU. If you have to handhold you have 10x more shake/movement than with a tripod (20 mikrometer vs 200 mikrometer)
"sharpness" of the lenses under ideal conditions would be 5 mikrometer... (100 LP/mm) which cannot nor need to be reached in real world
another idea off topic to this contaxinfo forum would be to adapt the hassy lens to a Minolta/Sony Alpha 100 body with super steady shot...