I own and use both mics for drum overheads, and a wide variety of other uses, as well as a pair of Neumann KM184's. Most of what captain 'verb has said is true, except I disagree that a matched pair of Oktavas are better than the C-4's. They are just different. The Oktavas are more colored than the C-4's, IMHO, and can be used by some folks as vocal mics, even. Do not expect much if you try this with the C-4's. I prefer the C-4's as instrument mics, and for remote stereo recording.
For overheads, the C-4's are clean and crisp and fairly neutral, especially good for jazz, pop, or country. The Oktavas rock on blues, metal, punk, etc. They just go with distorted guitars. They are good on cheap acoustics, as their color tends to airbrush the rough edges. Customer support is nil, tovarisch. Studio Projects support is as good as any in the business.
When you combine matching at a good price, versatility, customer support, shock mounts, a decent case, and omni capsules, I believe the C-4's are the better buy. However, you'll note that I like the Oktavas enough to keep a pair around anyway, even with the Neumanns in the cabinet. You pays your money and makes your choice.-Richie