All GeoTrust certificates are 128-bit. For each and every session, the server and browser negotiate and choose the highest common encryption strength between them. So if a 40-bit browser user hits your SSL-secured site, the resulting connection will automatically become a 40-bit strength encryption.
GeoTrust recommends that end-user Subscribers select the 1024-bit encryption strength or the equivalent descriptor option when generating their certificate requests. When the certificate’s key length is 1024 or longer, the SSL session key will be 128 bit. If the certificate key length is 512, the SSL session key will be 40 bit or 56 bit.