Andy,
I use a Chinese clone of the Noga you are on about (about 20% of the cost), and find it very satisfactory, but not perfect. Maybe the Noga one has a much finer adjustment screw.
With regards to base or head adjustment, both have their own negative effects.
For the base adjustment, because of the large moment effect of the arm, even a tiny adjustment on the base is multiplied greatly by the time it reaches the head.
With the head mounted adjustment, because it is on the end of a long arm, if you got the shakes, it is very difficult to make a super fine adjustment.
I never use a clock gauge, but a DTI with a swing tip, and almost always use the machine to do the very fine adjustments.
Not really what you were after, but it does give you a bit of an insight.
John