Poor performance after upgrade to 2003 Enterprise

We're running Citrix Metaframe 4.0 on Server 2003 Enterprise on an IBM HS20 blade server.  We upgraded this past weekend from Server 2003 Standard, and increased the memory from 4GB to 8GB.  Of course, added the /PAE switch to the boot.ini file.  (The upgrade also forced us to roll back SP2, to the 2003 Ent upgrade, then install SP2 again)....Ran all the Windows updates and upgraded to IE7 from 6.  We usually run about 50-60 Citrix thin client users on this server with out too much problem, except quite a bit of sluggishness, hence the upgrade to Enterprise to allow the added memory....Since the upgrade, the server is even more sluggish, forcing us to cut users'  ICA connection color depth from 16bit to 256 to speed things up, which isn't acceptable in the long term.   Windows sees the full 8GB of memory, but there's still over 5GB of unused memory.....double dual core processors are at 50-70%.    Any suggestions to speed up the responsiveness would be great.   Example of sluggishness: scrolling down a list can be very slow as the page visibly "wipes across" to refresh the screen.