What are the performance considerations between using a broad PK vs a separate synthetic key and UQ?
There is no significant disadvantage using the natural key as the clustered index


there are no non-clustered indexes
no foreign keys referencing this table (it is a parent row)


The downside would be increased page splits as data inserts would be distributed throughout the data, instead of at the end.

Where you do have FKs or NC indexes, the using a narrow, numeric, increasing clustered index has advantages. You only repeat a few bytes of data per NC or FK entry, not the while business/natural key.

As to why, read the too 5 articles from Google

Note I avoided the use of "primary key". 

You can have the clustered index on the surrogate key but keep the PK on the business rules but as non-clustered. Just make sure the clustered is unique becauuse SQL will add a "uniquifier" to make it so.

Finally, it may make sense to have a surrogate key but not blindly on every table: many-many tables do not need one, or where a compound key from the parent tables will suffice