Sounds like mostly gate delay? I'll share my ignorance. For metal traces on silicon the physical "speed of light in this material" propagation delay should only

Sounds like mostly gate delay? I'll share my ignorance. For metal traces on silicon the physical "speed of light in this material" propagation delay should only be around 9-10 ns/m. Call it 10 ps/mm, about 55ps in 5.5mm. Or else if the trace has high enough resistance (maybe not metal), another thing to worry about is charging the line capacitance. That is longer for longer lines, but it is a different kind of delay from speed-of-light.