as long as you don't have a bunch of stuff either not backed up or just don't know where the software came from, I would agree with the clean install, give your hard drive a fresh start, it's always nice, I format my hdd regularly and keep an external hdd for all my backup so I don't really need all the download, although it's a pain in my side, there's always things that don't go away when you delete and when you install over another update, go fresh if possible but to my knowledge it is totally possible to upgrade from vista ultimate to non ultimate win7...