加入nvarchar与int相比，性能差异有多大

I understand that join on nvarchar is slower because index is bigger as nvarchar using 2 bytes for each character but int is 4 bytes all the time. Is the join performance difference significant? Is there any strong reason to avoid join on nvarchar? I couldn't find any MSDN article about the topic.I understand that join on nvarchar is slower be