By default, the GetProcessInstanceList and GetActivityInstanceList web methods retrieve all the process data associated to the requests/actions.
If you don’t need process data values, you just have to add a SOAP header or querystring parameter: ShowData=False.
If you only need a subset of the associated process data, as of WorkflowGen version 5.6.2, you can specify the list of process data to be retrieved with the SOAP header or querystring parameter DataList (e.g. DataList=AMOUNT,APPROVAL,COMPANY).
This will dramatically improve performance.
Example of query string
http://localhost/wfgen/ws/ProcessesRuntime.asmx/GetActivityInstanceList?query=closed&datalist=REQUEST_SUBJECT,FORM_ARCHIVE