I don't think there are many Gnutella clients that you can actually ban that way. Ever since Shareaza has been open-source (and actually already before) it has been a piece of cake to circumvent that block. (If you don't want Gnutella clients to download from you, - don't use the Gnutella download mesh).

The reason Shareaza sources frequently fail is that they are simply overloaded. You are devoting a considerable amount of your bandwidth to creating and accepting TCP connections ( an amount of bandwidth that probably does not show in your bw statistics ) and sending busy signals, - not to mention that you hubs are flooded with UDP packets. As far as I can tell Shareaza's lack of responsiveness is mainly a design issue.