Use of either a Response (PclRESP) or the KeepResponse (PclKEEPRESP) parcel limits the maximum response buffer that can be indicated to the server to 64K, as size of 'MaxMsgSize' is only 2 bytes.
struct PclRespType { PclFlavor PclKind; /* 4 */ PclLength Length; /* 6 */ Int16 MaxMsgSize; };