In that case, either the Iwata CM or the Sotar would be good choices.
I think I would opt for the Sotar as the Iwata CM is REAL expensive especially for parts. With the Sotar you can buy needles or tips anytime but the Iwata CM has the head assembly machined as a unit for consistancy and you have to buy it as a set which, for example, runs $110 for the .18mm fluid head system for the CM-B and SB. [:0]
Of course if you were meticulous in taking care of it you may never need to replace this part.
Since you are considering an airbrush of this caliber I would recommend you call Dave Monnig at Coast Airbrush in Anaheim, CA.
Dave is the man to talk to about airbrushes and compressors and is considered one of the most knowledgable people in the country on them.
He is an Iwata man and will probably steer you toward them, although I don't know if he would recommend the Custom Micron for your needs or not. His number is (714) 635-5557. The web site for he and his wife's store is here:
http://coastairbrush.com/
Let me know what he tells you if you call.
Mike
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon