EIST works for me without affecting stability (LinX stable), however, C-State tends to make my system unstable(probably because it seems to lower my VCore by 0.01-0.02V)
i like EIST as it lower my vcore and speed while the proc is idling, and that's like 70% of the my comp uptime
so regarding ur question, yes a stress test is required after u enable power saving option, imo

This post has been edited by superpc: Jul 22 2009, 08:26 AM

EIST manages both vcore and multiplier(i.e. lower vcore and multiplier while idling, in my case i have 2ghz at 0.97V at idle)
c1e tries to switch off unused core iirc

i am pretty sure my c-state is off and EIST is lowering my multi instead of bus speed, while if C-state does nothing if it's on except from affecting stability
probably different function according to chipset i guess