How strong is the performance impact of singin when using RSA_AES_256_ECDH

To encrypt web communication, I use SSL with a RSA key with a length of 2048 bit, AES key's with a length of 256 bit and the ECDH-algorithm for the negotiation of the AES key's (or to exchange the DH-parameters to compute the AES key's).

As far as I understand, the RSA key pair's are only used the sign the messages for the negotiation of the common secret to encrypt the application data with AES (265 bit). Right?

My question: Which of these procedures got the most impact of the performance (cpu/ram) to encrypt a communication session with ssl? The signing of the DH-parameter by RSA by key-length? Or the AES encryption? How is the proportion to RSA signing by key length and AES encryption by key length?