Rick's got it nailed. Here's my opinion why. Depending on how many cubic inches you've got, and your intended usage of the engine I.E. mainly street driven, street strip, weekend warrior etc. and the rpm range your plan on running, will all dictate what head is going to work best in your combination.
Cubic inches and rpm range are going to require a certain amount of airflow to make the power thats wanted. Airflow usually comes hand in hand with port volume. Get to big of a head on your motor, port volume wise, and the engine doesn't try to consume as much air through the heads. This means that the air that is moving through the ports isn't moving very fast (velocity).
Slow down the air to much and lots of bad things start to happen. The fuel will actually start to fall out of the air charge and collect on the bottom of the runner just to be poured into the chamber is large drops which as you know burns much slower that small very fine particles. You also give up some swirl speed. The speed of the air fuel mixture as it swirls about the cylinder starts to decay after the valve closes and the piston travels up towards the chamber. Once again giving opportunity for fuel to collect. Than as the plug sparks and ignites the mixture, because it is moving slower, it takes longer to move across the chamber/piston top and you end up with some lost cylinder pressure which is what the whole process is trying to produce to begin with.
Get a head that matches your CID, and rpms and the power can go up a fair amount, and the torque can really take off. Now if, as Rick said, you've got enough motor, than these are a great head, if you don't, a smaller head will actually make more overall power.
Sorry it was so long winded. Hope it helps.