Ciphering procedure is done during the SDCCH phase, meaning that the MSC and the MS agrees on a certain ciphering algorithm. When you say “no ciphering”, it actually means that the A5/0 is going to be used.
The amount of messages on the SDCCH phase is the same, whether you use a5/0 or a5/1.
As said by Fedem, the ciphering itself is applied locally by the BTS and the MS, with no (or little?) effort from processors.