Hi Trevor, thanks for the info. I still only see updates coming in every .4 seconds (the data is timestamped at seconds 0.0, 0.4, 0.8, 1.2, 1.6, 2.0, and so on), essentially 2.5Hz. I'm viewing the data both with Garmin's sensor config utility, and VisualGPS.

If it works, though, it works -- I'll hook it into the EFIS when it arrives from the dealer and see what happens. It only raised my eyebrow because I seem to remember reading that the 5Hz gps's were preferred as it made the synthetic vision and mapping displays smoother.
Thanks, Joshua