Systems and methods for monitoring the performance associated with fulfilling resource requests and determining optimizations for improving such performance are provided. A processing device obtains and processes performance metric information associated with processing a request corresponding to two or more embedded resources. The processing device uses the processed performance metric information to determine an allocation of one or more domains to be associated with the two or more embedded resources. In some embodiments, in making such a determination, the processing device assesses performance metric information collected and associated with subsequent requests for the two or more embedded resources using each of a variety of alternative allocations of domains associated with the two or more embedded resources. The processing device may also consider a number of factors, including domain selection criteria obtained from an original content provider. Aspects of systems and methods for generating recommendations to use a particular allocation of domains to process a subsequent request corresponding to the two or more embedded resources are also provided.