The size of the TPC events rises with luminosity in pp500, due to pileup.  Below is one measure, using the JP2 events, which do not have FGT readout. Projected maximum luminosity from C-AD is 200 x 10^30 cm^-2 s^-1, which is ~700 kHz ZDC coincidence rate (some nonlinearities will come in for singles and doubles corrections at this point, and I don't have a great model to use to project the level of corrections needed).  Note also that a central Au+Au event is ~1.2 MB, so we're talking about twice as many hits in the TPC.  

So, I take this event size, and plug it in with a given maximum rate that the DAQ can push from TPX, subtract off the rate of W triggers (assumed to be 30 Hz/100 kHz ZDC), and get a rough projection of the event rate we have available for other triggers.  If we are limited to 500 MB/s, as we were in Run 11, there is essentially no space for other triggers.  However, it does appear that the limit is somewhat more relaxed this year; may be closer to 900 MB/s, or even higher.