The FSUIPC "mapping" of button to simconnect variable id, then the simconnect variable id mapping to Mindstar gps. is only done once [off-line] as part of the installation of the Mindstar G5330 and Emuteq.
During a flight, when an Emuteq button is pressed or a knob is turned, that is a USB event that is processed by FSUIPC, and passed to Mindstar. So the question becomes, how often are buttons pressed or knobs turned? Well, since I have to enter a flight plan manually, and that requires lots of knob "clicks", that can take a tiny percentage of time over several minutes times your frame rate, and you won't notice it. [i don't think I can turn the knob faster than about 10 clicks a second [read that as selecting a letter for the waypoint ID. So going from A to K might be done as fast as a second, then it's click to the next ID position, and repeat for the next character, etc.
What you really want to ask is, "with the Emuteq set up as a separate display [e.g. using NVIDIA Surround], how much processing is being done 1) by the video driver, and 2) by the emulated GPS ? And for that, I defer to Mindstar. [i was previously using Emuteq with the built-in GPS, all I'm doing is replacing the built-in GPS with Mindstar's. This is different from no GPS to virtual-cockpit GPS, or no GPS to Emuteq with built-in GPS, etc. So for performance issues, you will always need to specify what is the "before" and what is the "after."]]
If you're really performance squeezed on your main computer, there is also a remote capability via simconnect, where a secondary computer drives the Emuteq. I will probably be doing that since I already use remote simconnect with SPADnext to drive several Saitek panels/instruments as well as the FSWidgets GMapHD moving map. Remote "off-loading" means no video driver resources taken on the main computer, and minimal processing to support some gps interaction via simconnect data generation/transfer, the bulk of the GPS processing/display generation will be done on the secondary computer.