Yo Kensington! Why the C-4's? In many ways, RobertD touched on the reasons, and his comparison was a balanced one. First, let me say that I am quite familiar with MXL 603, but the 604's I have not used on acoustic. On some other sources (violin and viola) they sounded pretty much to me like the 603's, but with available omni capsules. I think most of what RobertD said was true, and nonetheless, *I* prefer the 603's to the Oktavas, which I also own. Just goes to show you- as he said, not all guitars are created equal, and not everybody is looking for the same sound.
His comparison of the 603 to MC012 illustrates exactly why I like the C-4's. They have the high-end detail of the 603's without the sometimes brittle high end, and are darker than the 603's, but not as dark as the Oktavas. They split the difference, and in my opinion, are more truthful than either of the above. In my opinion, they are very similar to the SM81 for those reasons. I like the Oktavas for violin, where I want to scrub off some scratchy highs, and for classic rock overheads. For acoustic, I mostly use Neumann KM184's, which produce more high end detail than any of the above, without annoying harshness. I put up the C-4's when I just want a middle-of-the-road honest small diaphragm condenser. I often use them for remote stereo recording of live acoustic, classical, world music, a barbershop quartet, bagpipes, whatever.
Are the Peluso's better? No clue, I've never used them, but a lot of people think they are very good middle-of-the-road mics. Are the Josephson C42's better? Yes. I *have* used those, and they are *very* good middle-of-the-road mics. But- they aren't $300 a pair. I do a lot of stereo recording, so I would be unlikely to ever buy *one* small diaphragm mic. Hope that helps-Richie