[Brian]

If you are using Intel (Altera) FPGAs such as: Intel® Stratix® series, Intel Cyclone® series, MAX® II, MAX IIG, MAX IIZ, FLEX®, ACEX®, APEX™, Mercury™, and Excalibur™ devices use the speed grade to indicate the relative performance of the device.

 

Devices with low speed grade numbers run faster than devices with high speed grade numbers. For example, a Stratix® III FPGA with a three speed grade is the fastest available Stratix III FPGA.

 

For Xilinx FPGAs, each package has a speed marking from 1 to 3. 1 is the lowest speed and 3 is the fastest speed.

 

Use the tools to check your timing margin, based on that data you will be able to choose the right speed grade for your project