I prefer GPH over PSI. PSI can be adjusted as needed where volume/demand cannot. If the engine wants or needs more, it will be there and only use what it needs. Too much PSI will blow the gas right passed the needle and seat.

Depending on your application, the modifications necessary to install an electric pump would also add to the cost of the install. Most electric pumps (Holley, MagnaFuel, etc.) would need to have the fuel line cut and installed in the rear. Those types of pumps are a push style and do not pull the gas from the tank very well. They work best in a gravity fed situation. A mechanical pump mounted on the engine is a pull style pump and will pull the gas from the tank. I would personally go with the mechanical at 120 PGH as long as it is a quality pump.