Should I create 2 different databases if they would keep 70% similar data?

I am writing a microservices based NodeJS-Cassandra application and I haVe few services they would need 70% similar data( like username, avatar, videos, etc.) and I am just wondering to know is it a good idea that I create 2 databases like: DB1: > A,B,C,D,E,F,G,H,I,J,K,L,M,N DB2: > A,B,C,D,E,F,G,H,I,J,W,X,Y,Z Or just create one database like: > A,B,C,D,E,F,G,H,I,J,K,L,M,N,W,X,Y,Z I know from microservices concept that we should give it's own database to each service, but as long as my data contains some massive data like video files, I don't know what should I do in this specific case? I like to know if there is any rule of thumb says **"if your databases would have more than x-% of similar data, or the data you should replicate in both databases exceeds x-GB, it's better to keep them in 1 database"**?