Is there a difference in the sensitivity of adjustment between the barrel adjuster on the rear derailleur
vs. a downtube cable stop adjuster with the adjustment wing??

I would have to believe that the downtube adjuster is a bit more coarse than the barrel adjuster,
but I am not sure.

not really .. thing is the one on the rear is where you can watch its effect as you turn it , on the repair stand, turning the pedals..

They are almost 6x1mm or other close x1mm threads so 1 turn = 1mm of cable length adjustment.

You can get metric bolts in other thread counts (depending on the diameter) like .25, .50 and .75, but they are rare on bicycles.

See this article for the effect of a 1mm cable length change.

https://blog.artscyclery.com/science-...compatibility/

You can adjust the barrel adjusters in less than 1 turn increments,tho.
There is sometimes an external star wheel on the adjuster in order to make it easier to
turn the barrel, and those are usually detented in half-turns (?).
Are nit the downtube adjusters, which have stepped ramps, a bit more coarse?

Actually Shimano and Campy adjuster threads are M5. 5mm diameter by 8 mm per thread. So one turn produces .8mm cable length change, whether done at either end of the cable. Some in line adjusters do use a M6 thread. Andy.

the M6 are less likely to break off.

But M6 don't come on most ders, shifters or frame stops which are found on most bikes. Andy.

The downtube cable stop adjuster for the rear is not threaded; rather, it has a stepped ramp that has 6 or 8 positions available.
Anyone know the incremental change for each of these ramp stops?

Just leave it centered and do your fine adjustment at the RD. These are for quick adjustment when swapping wheels during a race. IIRC on some of them the ramp assembly can be removed and replaced with a traditional adjuster.

Use calipers to measure.

(Headslap) DOH !