I grabbed the a plot of the iLIGO PSL frequency noise spectrum from the Rana manifesto:
Rana's contention is that this spectrum (red trace) is roughly the same as for our NPRO.
From the jenne/mevans/pepper/rana paper Active noise cancellation in a suspended interferometer I pulled a plot of the calibrated MC_L noise spectrum:
The green line on this plot is a rough estimate of where the above laser frequency noise would fall on this plot. The conversion is:
L / f = 10 m / 2.8e14 Hz = 3.5e-14 m/Hz
which at 10 Hz is roughly 1.5e-11 m. This puts the crossover somewhere between 1 and 10 Hz.