I was curious so I did some quick back of the napkin calculations.
Compression is maximum near 13.5Hz at about 3.8dB during the 103.8 volt sweep, which is exactly where we would expect the velocity to be the highest based on the models. By simply using the voltage applied in a simulation and allowing for 3 to 3.8dB less output from 12-16Hz after compression, it looks like the MAUL was producing about 30m/s or so during the 103.8volt sweep.The 185 volts sweep had the amplifier current limiting severely so it is hard to tell how much of the extra compression was partially the amplifier. Regardless a quick velocity estimate is a maximum of a bit above 40m/s. We don't have burst data for 13.5Hz which is the worst case scenario for velocity for the MAUL but a quick look at the maximum levels at 12.5Hz and 16Hz compared to the 103.8volt sweep results in an estimated 45m/s at 16Hz and 61m/s at 12.5Hz. I did consider the flare-it program when designing the MAUL and it suggested chuffing at 37m/s and core limit of 80m/s for a 12" pipe.
This is all very rough work but based on this I think it safe to say that the vent has not completely brick walled at 50-60m/s but is heavily compressing the output by 7-8dB at that point and for all practical purposes may be "there". Huge increases in input power to the drivers will continue to produce less and less output increase from the vent. Of course this is also at quite low frequencies down near 12-16Hz too so that should be considered. Yes this is accompanied by significant air noise as well. Maximum velocities in the short horn section are only an estimated 20-30m/s.
It might be worth a look at some other vented system tests to examine the compression behavior and guesstimated vent velocities.