Here is a write-up I did before to answer this question:
EVē vs. Performax™
The Performax and EVē series share many attributes: Stepper motor movements, LED backlighting, and solid-state sensors. The EVē individual gauges cost more than the Performax counterparts, since the gauge must contain the processing power, while the Performax processing power is mostly in the ESP controller. The Performax series uses an underhood controller (the ESP) which connects to all the sensors (so you don't have to run all those sensor wires through your firewall). There are 3 common wires which run to all of your gauges (up to 17 total), simplifying your wiring and allowing you to move gauges around to any location. The Performax system also includes the Total Recall™ feature, which provides the ability to view the extreme values of all functions connected to the Performax system. For most functions, the stored value is the maximum value, but on fuel system pressures (Fuel, HPOP, and Rail Pressure), the lowest value while under load is recorded (requires the use of Performax boost gauge sensor). This allows you to focus on driving down the dragstrip or pulling track, keeping it in the groove instead of trying to see if your fuel pressure is dipping at the end.
The ISSPRO Performax PC Datalogger is an optional interface module and software package which allows your Windows-based PC to record all of the data being read from the sensors connected to the Performax ESP controller.
The module connects to the gauge wiring in place of one gauge (or you can wire in an additional gauge connector in a convenient spot for the module), then connects via the included cord to the USB port of your PC.
The software displays actual values for all sensors connected to the ESP while it is logging (there is a start/stop button on the screen). When logging, the software writes to a comma-separated-value (CSV) file to be opened up in Microsoft Excel (or a similar program). The data is logged for each channel at 5 samples per second. You can use your spreadsheet (e.g., MS Excel) features to analyze and graph the results.
The data is logged for all sensors connected to the Performax ESP, regardless of whether a corresponding gauge is installed. You can have all 17 channels connected to sensors for datalogging, even if you only have room for 3 gauges in your truck.
If you are not interested in the Total Recall or PC Datalogger features, then EVē is the likely choice when installing 3 or fewer gauges. For more gauges, the Performax system is more cost effective, especially when installation time is taken into account.