
I did this portrait of my daughter with a hp-cs, at that size (slightly smaller in fact as I made a little border). It's no where near as good or detailed as most portraits, but it is all freehand with no masking or shielding and I was pleased with it. I haven't ever used an infinity or a micron (The micron will be mine.....one day), and I know they are capable of much finer detail, but the hp-cs worked great, and pulled great lines for the hair, eyelashes etc.
I can't do photorealism, and this is nowhere near, but I think that is my lack of skill rather than the airbrush. So I guess it depends on how much fine detail you would like to achieve. I don't get the time to paint portraits as I'm usually painting bikes, and so haven't pushed the hp-cs to it's limit detail wise. I can't afford a micron right now, so I guess I'll see how far I can get with what I have. But I guess everyone uses the infinity or micron for a reason right? I want one because I think I will be able to paint better with it. It's a lot of money to spend on something if you aren't sure airbrushing is for you, but if you know you're hooked, and the kind of work you're aiming for is high detail, and you have the moolah, then I would go for it if I were you.