Dedicated Inputs/Clock Pins vs IOE inputs
A dedicated input pin or dedicated clock pin does not have the IOE logic. The input timing is specified as routing delay only:
Tincomb + Tsamecol = 3.1ns + 1.4ns = 4.4 ns
Use dedicated input pins to minimize input delay. Not many on device - 10K20 240 pin package only has 4 dedicated inputs and 2 dedicated clock pins.