#4 is defintely from the breakup of the Soviet Union. It looks like it's a local overprint from the post office in Konotop, Ukraine. There are so many 1991-1992 soviet overprints in Ukraine, you could fill a whole album with them alone.
Here's the Wikipedia article on Konotop:
http://en.wikipedia.org/wiki/KonotopYou can see the city seal in the center of the stamp overprint.