How to test the speed grade of the FPGA

How to test the speed grade of the FPGA,I use V2-6000, speed grade is -6,but I doubt that the speed grade can't reach -6,So I want to know how can I test the speed grade?3X.

The speed grade is the speed grade, there is no "checking" it. The speed grade is decided by the part when it is manufactured. IIRC, all the parts are manufactured the same, with the higher quality (ie speed grade) taken from a specific area of the wafer (or they are tested?).

You might be able to push the part faster than the speed grade says, but it's not guaranteed to work.

back in the days of V2 Xilinx used to test all the devices (don't know if that is still true) as they are reprogrammable. They would bin the parts according to speed grade based on passing tests for that speed grade. Unless you can find someone on here willing to divulge Xilinx proprietary information I doubt you get much information on the test code used to run those parametric tests on the die to bin the parts according to speed grade.

If the part doesn't behave correctly at a speed which the STA tools say it should meet timing, then given the age of Virtex-II devices, introduced in 2001 (though they still claim to "produce" them to support old designs...probably just have a bunch of left over die), I'd be more inclined to think they may have been damaged by ESD from poor handling. ESD doesn't necessarily just kill a part usually you'll end up with degradation of the performance in some fashion.

Reduce supply voltage to min and test for margin at speed with your design.
Avoid metastable or race conditions use synch clock for critical timing.
Poor design choices can obviously reduce speed integrity issues.
Raising voltage 5~10% can make marginal designs sometimes work....at room temp or colder.