For Virtex-II Pro, the characterized timing should not change when the voltage is prorated; however, in the 6.3.3i Timing Analyzer software, varying the temperature causes changes the timing. Leaving the numbers at the default settings gives you the same numbers as running command line. Changing the voltage to either 1.425v or 1.575v causes the timing to slow down and fail constraints. To get the correct worst case numbers, you need to change the voltage to 1.4V.
In timing analyzer the temperature can be set to 1.4V to get the worst case number or TRACE can be run via the command line at any of the voltage settings to get the workcase number.