OK, with Excelsior's drop in category, I now have a delimma.
I currently have a 5 night stay over Christmas for 2 rooms at the St. Regis (using C&P awards). But with the Excelsior dropping to a Cat. 5, it could get 2 rooms there for 15K points and $600 less for those same 5 days. I assume there is a reason why the Excelsior has dropped. But when I look at both of their rates over my stay dates, the rates aren't that different.
Based on reviews I had decided that the St. Regis would probably provide a bit more of a memorable stay, but I'm not sure it would be worth the extra points and cash for it.
Note I'm traveling with my family (wife and two teenagers) and none of us have been to Rome before (and the rest of the family has never been to Europe before either.)