A packet capture on the client or the BIG-IP might help (look for the ServerHello message), however, the client sends a list of it's supported ciphers and the server selects just one (normally the most secure) so unless you can configure a client to specifically use a cipher you have blocked it doesn't prove much.
That being the case perhaps you should clear the statistics here: Statistics > Module Statistics > Local Traffic > Profiles Summary > Client SSL just after the change and then open some connections and observe what Protocols etc are used. It still doesn't prove much unless you can get a client to connect requesting a known blocked cipher.
A better method might be to configure a ServerSSL profile with the cipher string you want and observe what ciphers it presents in the ClientHello message it will send to a host. With this, you can obviously test before the change too. But you might not consider it valid as it's not the actual ClientSSL profile that you'll be changing.