You could add an XmlLoadOnDemand mode that mix the virtual and other modes....

 One that could load like virtual mode, but act like sync....

Ex.:

If you have an DB with 1000 rows, you could set the rowRange to 100 and then if the grid size is set to see only 10 the user can scroll to see all the 100 rows without a post back(and the view state could mantain the data updated by the user)....when the user tries to put the 91 as the topRow then the grid loads another 100 rows (starting in 91...because he could not see the 100º row)......I think that mode will be realy good when binding to larger data...