I'm trying the program-background and program system cache options(winxp)
I set for system-cache and rebooted and they play well again, but something may change, probably/usually when Boinc project focus changes. ( climate prediction uses big cache )
I still believe that the background option will do something permanent if anything simple is to work.

Idea from this link:
http://www.mdgx.com/newtip16.htm#CPUPR
- my Win32PrioritySeparation was still at 2 after system-cache change.