If I'm on fast path then presumably G.INP is not needed but equally I wonder what happened to the interference that was affecting my line at first.
I have never had interleaving on my home connection and have had long, stable connection times. Attainable rate and sync dropped as crosstalk increased. I now have G.INP and am synced at 80000/20000 from the most recent pre-G.INP rate of about 75000/20000.
The answer was yes! I did get G.inp and actually it's quite a good boost.