Bottom line; the'yre pretty damn close to each other in sound. The Studio Projects C1 is a little hotter (about 2 dB more output), and a little quieter (again, by about 2 dB). Overall, the frequency response is very similar, with maybe a -1dB shelf around 800 to 1,000 Hz on the Studio Projects C1. The Marshall MXL-V67G sounds slightly fuller, but again by a very small amount.
So, is there a clear-cut winner? Nope, they're both really nice mics that will do a pretty good job for vocals where you're looking for a full bodied, rich vocal sound. They're both retailing at around $300 with a street price of right around $200. The Studio Projects C1 is heavier and looks like the Brauner VM-1 mic while the Marshall MXL-V67G has a distinctive AKG C12-VR look and is not quite as rugged.
They're both pretty good values for the money.
One warning before you run out and plunk your money down on a C1:
This is only a preliminary test. I've only heard this one mic so far. Quality control and consistency are big problems with Chinese and Russian microphones. I
surprised Alan Hyatt today and asked him to send me another set of the mics to see how close they all match each other. I know the Marshall MXL-V67Gs are consistent, but I can't guarantee that's also true of the Studio Projects C1 - al least, not yet.
If you have $200 burning a hole in your pocket and you can't wait to run out and buy the C1, you probably won't go too far wrong, but I can't give it a sweeping endorsment, until I'm certain that your C1 will sound the same as the C1 I just listened to.
But so far, it "looks" like it's gonna be another winner in the low cost, big mic race.