Keep the oktavas and learn to use them properly. Room, source and placement are often more important than mic (and certainly in this case, between oktava and B1's).
I have both. The oktava's are more faithful to the source, and I believe they have a better transient response since they are SDC and not LDC.
The B1 will give you a bit brigher sound and probably a bit more distortion (which also adds high frequency contents -- can be good on certain things, sometimes). They will sound slightlly "larger than life" when compared to the oktavas.
However, they will be more difficult to place. They have more off-axis coloration than the oktavas, and hence the room and placement can colour the sound more, and needs you to get up even more than with the oktavas.
The oktavas, on the other hand, have a wider pickup pattern and I think less off-axis artifacts. This makes them probably a bit less critical to position in relation to the kit you're playing, although they may pick up as much/more room sound.
For other sources, both will work, including guitar. With a good pop-filter, the oktavas are pretty decent on voice also. A good addition to the C1, when you need a slightly darker vocal.
I'd say: keep them, and get a B1 later if you need it. Or maybe forget the B1, and get a different type of mic instead (Røde for a "bright" sound, maybe ADK, MXL for darker sounds).
-- Per.