Speed grade
No, you misunderstood my correct but unclear answer. I'll try to clarify.
In the old days, the speed grade of many PLD or GAL devices would directly tell you the performance. For example, -4 -5 or -7 would mean 4ns 5ns or 7ns.
Modern FPGAs speed grades usually don't have any intrinsic meaning like that. Now they are simply code numbers that you must look up in the AC Specifications section of the data sheet. The data sheet gives columns of timing parameters for each speed grade. Some FPGAs have hundreds of different parameter values for each speed grade.