Single Database or Multiple Database

Dear Informixer, I am doing a project(A) which needs to access data that currently scattered in several different INFORMIX databases(X, Y, Z). Those databases were designed for some other projects(B, C, D) and work well. But, from the new project (A) point of view, it make sense to have all data be integrated and stored in one single database(W). This way there is minimal redundancy and integrated information may easily be get by joining tables within the database(W). Agreed? My question is which is a better solution: Single database to contain all kinds of data or Multiple database to handle data of some specific area? If you think Multiple database is the answer, what is the normal way to get information which will get by joining tables resides in different databases? If the Single database is the answer, How will the performance be affected, since the database is shared by more applications. This question might look easy for you. But please help me to make the right choice. Thanks in advance. Wendy