What (apart from the obvious) is the difference? is one better than the other? I think i'm right in saying the standard ecu can't use low unless using some sort of ballast resistor???

Does one type flow better? more consistent??

If it makes a difference, i'm looking for 400-450 ponies using stand alone management that will work with either (amongst a LOT of other EXPENSIVE things... :(

I can't remember the difference offhand, but I think there was something on the subject in the Practical Performance Car that had the feature on tuning R-100 series and Estelle/Rapids.

There was almost certainly a feature on how to calculate how much fuel flow you need to achieve a given power output, which sounds like it would be useful to you.