Flow numbers will tell you very little about how a given head will make power.
The first thing I learned about flow testing was a straight flow test means very little.
That's why you can lose "flow" and gain power. Remember the old saw about "it's not about the size, it's about the shape"? It's true.
Two ports can flow the same at say 28" but one head will beat the other up on power. It's all about the shape and it starts with the valve job.