I watched a video from Sema that a Holley rep did, and he stated the four injector unit supported up to 600hp, when I look at it on line it states 650...my engines should be right at the end of what the 4 injector will support, whats the truth ?? 600 or 650.

this was on line

Bolt on carburetor replacement (designed to fit single & dual carb manifolds)
Throttle body mounted ECU - no extra boxes to mount
Supports up to 650hp (4 injector version) and 1250hp (8 injector version)
4 wire vehicle connection (Battery +, Battery -, Switched ignition & RPM)
Integrated fuel pressure regulator
Integrated ifnition timing control & coil driver
Color touchscreen for setup and gauge views
Self-tuning ECU means you don't have to be a computer/tuning wiz to have EFI!
Black Finish
Sold Individually

The hp rating is just based off of the injector sizing. Theoretically it will support 650, but depending on the bsfc, and airflow requirement of your combo it might be less.