SP level for TermServ and Metaframe

I have a network running a DOS database on NT 4.0. Several NT clients were crashing. SP6a fixed a memory leak in the DOS VM. I have some WinTerms running ICA client on a NT Terminal Server with Citrix Metaframe 1.8. It looks as if they leak mem and run up the TS CPU utilization to 100%. I checked the service pack on the TS and it looks like it is SP4. Not sure about the Metaframe. Microsoft website is not clear if SP6 is stable and Citrix website said I needed to buy a license for their SP3. Can anyone suggest a *stable* service pack level for TS and Metaframe for DOS/MS Office apps?