It's really impossible to say based on the information given. It depends on the width of the table and existing indexes, whether the existing PK is a good candidate for clustering (narrow, stable, monotonically increasing), the typical access patterns (singleton lookups versus range scans), level and type of update/delete activity and more.

Do you have a problem right now that you are looking to solve, or do you just wonder if making the clustered table would improve something (and what might that something be)?