Just to clarify, this is why the 904 "consumes less power" or, there's less engine horsepower loss through a properly built 904 because of the smaller, lighter components and less internal friction.
I'd suggest making your choice based on your intended use. Primarily race, then go with a built 904 to maximize power to the pavement. But if almost always a street car, I might think more about the 727 since they're basically 'bullet-proof' if built correctly.
Consider all the options and then choose wisely.