Ok... So looking at IFG as 96 bits or 12 bytes of "overhead" thats 0.8% or 0.13% for 1.5k and 9k frames. Why do I care about 0.67% of throughput? And pretty much all silicon in over a decade does line rate at 1k anyways. Or if its latency a hypothetical higher clocked lane would be something like 1ns instead of ~3ns per frame? Thats the difference between 2 clock cycles and 6 cycles of latency.

So what is your shorter/faster ifg buying in practice.

I've seen an audio bus that had to shorten the gap to have enough bandwidth, but that was with 100mbit.