GT-40Ps weigh a lot more (50-70lbs) than comparable aluminum heads. You can't just compare flow numbers with flow numbers. What is it, 100 lbs cost you a tenth in the quarter? It's also weight in the front which is where you don't want it.
You can run more timing advance with aluminum heads since they dissipate heat better than iron heads.
Unit's right about the TFS heads. They're the best bang for the buck.
As far as torque goes, it depends on the cam and the length of your intake runners. TFS TW heads have no problems with low end torque and are great at the high end.
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351W 89 Mustang GT Convertible