I'm working on an application that'll have two separate client EXE files. However, both projects share some same middle-tier classes and I'm asking some advise on pros/cons of two approaches.

1. Create unified middle-tier DLLs (one business objects DLL and another Data objects DLL) for use by both EXEs.
2. Create separate middle-tier DLLs (2 BO, 2 Data)

I would think approach 1 has installation and deployment advantages to approach 2's flexibility in maintenance and upgrades. What do you think?