I have used DesignSpace for analyzing assemblies (up to 15 components). I am using DesignSpace on a 2.4GHZ PC with 1GB RAM. If the contact between the components can be represented as a bonded (glued; no movement) contact, DesignSpace handles very large assemblies without any problem. However if frictionless contact is used, computation time increases very fast with number of contacts.
Therefore the trick will be to model your assemblies properly.