if the list contains less than 5000 items, the performance of the CQWP is likely to be very good. However, if the list exceeds 5000 items, and the query in the CQWP is complex, the Web Part can run into performance problems. It’s difficult to define exactly what a complex query is, but a Source that goes across all sites in your site collection is more complex than a Source that queries a specific list. Also, if you query uses Additional Filters, the query complexity increases. The query complexity increases depending on the site column types and conditions that you use. Here are some examples:
A query that filters on a site column of type Multiple lines of text is more complex than a query that filters on a site column of type Yes/No. A filter that uses a contains condition is more complex than a query that uses an is equal to condition. Multiple Or conditions increases the complexity of the query
The performance of the CQWP is also affected by where your content is stored. If your content is stored across several sites, the total amount of list items the Web Part has to process will affect its performance. For example, on your company’s home site, you want to display the latest news items from lists that are maintained in multiple subsites. Each list contains 1000 items. That means that the CQWP will have to query across 3000 items.
Below is the link where all the content above come from. The article is comparing Content query webpart and Search Query webpart where it highlight the advantages of Search Query webpart over Content query webpart which i think answer your question regarding performance of using Content query webpart.
Since your environment is SharePoint 2010 i would not able to recommend Search Query Webpart.