I believe this would have positve effects on setup timing but not sure how much - I am currently rewriting some functionality for this and setup timing is violated according to TimeQuest.
From the datasheet of Cyclone 4 ,the maximum voltage for Vccint maximum voltage is 1.8V. page no:2 of the datasheet
So may be that is the reason for the device is not going bad,
setup timing is violated according to TimeQuest
What is the violation