I have an AirBrush City MA-1000 compressor (idnetical to the Silentair Scorpion I model) for many years. It is typical of the starter compressor with this spec:
http://www.silentaircompressor.com/scorpion.html
For the low end Scorpion I model, notice that it says Max pressure at 30 psi and 0.7 CFM. Both are true separately, but it is NOT 0.7 CFM at 30 psi. When I fully depress the trigger on the Iwata HP-CS (0.3~0.5 CFM), the pressure drop to 11-12 psi. It works ok most of the time, but there are restrictions. It does not work well with my old external mix, siphon feed airbrush when I want to spread larger area.
I wanted to upgrade to a compressor that can sustain full airflow at 40 psi or higher. I tried Paasche DA400 airbrush compressor and a Dewalt D55140 tool compressor.
http://www.paascheairbrush.com/compressors_da400.html
http://www.dewalt.com/us/products/tool_detail.asp?productID=15513
The Dewalt is slightly cheaper, has a tank and provides a lot more air at higher pressure. I ended up keeping the Paasche DA400. The difference is 10 dB in noise level. The Dewalt is not loud (71 dBA). You can still hold a conversation with only slightly raised voice. I am sure some will find its noise acceptable. (Some reviews of the Dewalt on the internet called it whisper quiet. Not really. When I tested it at Home Depot, it was much quieter than any other tool compressors, including the larger Dewalt's, in the store.)
The DA400 can keep 50 psi at the full blow HP-CS. No pulsation. The motor is on at 90 psi and off at 65 psi. Using a 25-ft nylon hose, I am able to get reasonable duty cycle from the DA400 without a tank. Among all the AB compressors tested by Fine Scale Modeler in the July issue, the DA400 has the largest steady pressure range. It was rated at 1.48 CFM at 20 psi and suposed good for two airbrushes. The noise is 59 dB, not the extra quiet type (<40 dB), but very tolerable in door. I will like to fit a small air tank (<1 gallon) to this compressor if I can find one at reasonable cost.
When shopping for compressor, make sure that you have enough air flow (0.7 CFM for each AB) at the pressure range you want (10-50 psi?). Many compressor manufacturer of cheap model will spec max airflow at 0 psi and max pressure at 0 CFM to mislead buyer. Be ware.
The above is the experience of myself on two compressors. Very limited samples. But I hope it helps others who are looking. The final choice is an individual matter.