The size isn't likely the problem. When looking through your trace, I see that the "protocol" field in the "virtual_server" structure being returned in the result array is empty. In a response from my system I get the value of "PROTOCOL_ANY" returned.
xmlns:E="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:A="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:s="http://www.w3.org/2001/XMLSchema-instance"
xmlns:y="http://www.w3.org/2001/XMLSchema"
xmlns:iControl="urn:iControl"
E:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"> xmlns:m="urn:iControl:LocalLB/VirtualServer"> s:type="A:Array"
A:arrayType="iControl:LocalLB.PersistenceRecord[][1]"> A:arrayType="iControl:LocalLB.PersistenceRecord[1]"> s:type="y:string">DC5 s:type="iControl:Common.IPPortDefinition"> s:type="y:string">10.10.10.221 s:type="y:long">80 s:type="iControl:LocalLB.PersistenceMode">PERSISTENCE_MODE_SOURCE_ADDRESS_AFFINITY s:type="y:string">192.168.44.149 s:type="iControl:Common.VirtualServerDefinition"> s:type="y:string">DC5 s:type="y:string">172.27.11.117 s:type="y:long">0 s:type="iControl:Common.ProtocolType">PROTOCOL_ANY s:type="y:long">1295440156 s:type="y:long">11
I looked trough the sources and in 10.0 this value was omitted in the response generation but it was fixed in 10.1 and above. This very likely could be your problem. I don't have a way to test this as I don't have access to a 10.0 build, but I'm fairly confident that upgrading to 10.1 or above will fix your issue with this method.
-Joe