Yup the normal level used will knock around 10-12mbps off the ds sync rate and add 7-8ms of extra latency
I think we should perhaps look at the effect of interleaving more in percentage terms.
When my connection had attainable rates of around 33 Mbps, interleaving depths of around 400 or so left me with sync speeds of around 30 Mbps.
More recently, with attainable rates of around 23Mbps, Interleaving left me with sync speeds of around 20.5 Mbps.
So for my connection, at lowish interleaving depths, the effect was a syncs speed reduction of around 10%.
With attainable rates of say 90 Mbps, 10% reduction would equate to a possible sync speed of around 81 Mbps, capped at 80 Mbps = 10 Mbps sync speed difference.
Higher interleaving depths than around 400 (say 1000 or so) would no doubt show a larger sync speed reduction?