1. A method for adjusting tuning settings based on an attribute of a client, the method comprising: (a) identifying, by a device intermediary to a client and a content server, a policy for evaluating the client responsive to a first request of the client to access the content server, the policy specifying an expression comprising a clause to be evaluated by the client to identify an attribute of the client; (b) transmitting, by the device to the client, a second request to the client to have the client evaluate the clause; (c) receiving, by the device from the client, a response to the second request, the response comprising the attribute of the client; (d) receiving, by a server intermediary to at least the client and the content server, the attribute of the client from the device, the server comprising tuning settings for improving performance of communications of response data from the content server to the client; and (e) adjusting, by the server, the tuning settings based on the attribute of the client.