Hi there
Is 11mbps the wireless connect speed or throughput? If it is through put then that may be about right for a basic adhoc wireless network connection. This is because standard wireless is half duplex. Even with a standard access point and one client the max throughput is only about 22mbps when connected at 54mbps. I don't think adhoc mode has as good control over the data flow as an infrastructure wireless network so 11mbps might be it.
Cheers
Dale