HFM Subcube

Hi all the HFM experts!! We all know how important Subcubes are and its impact to design. I want to ask what impacts more - having a large Number of Subcubes (due to large number of entities) or the size of Subcubes (stored data records for subcube dimensions due to large number of  Account C1,C2...) .?

We have a large 11.1.2.2. application  with 6000+ entities. If we decided to move the lets say 5000 base members to a new custom dimension C5 , our understanding at high level is that we are reducing the number of subcubes but the subcubesize will increase as we will have new custom dimension with 5000 members so there may not be any benefit. I may be quiet wrong but can someone throw some light and we can have a knowledgeable discussion