The aluminum heads are of improved port AND combustion chamber design, CK. All the porting work you might effort to do on a set of iron heads will not allow you to obtain the horsepower and torque curves that can be obtained using John and Geoff Mummerts' new cylinder heads.
For strictly street use, you may not feel the new heads to be worth the cost, especially with what you'll have to pay to have them shipped to Australia.
My understanding is that the improved cylinder head flow is at all rpm speeds, but really shows its benefits when engine speeds exceed 3,500. The dyno charts are in the Forum archives from the extensive comparative tests that Ted Eaton did with iron heads compared with the new aluminum heads. And if you want still more capability, JM offers CNC ported aluminum heads for competition purposes.
Yes. Because aluminum heads dissipate heat more rapidly than iron heads, you can run a slightly higher static compression ratio than you can with iron heads without detonation problems. Remember though that your engine's dynamic compression ratio, which is related to when the intake valve closes, ALSO is an important factor in whether or not you will encounter detonation problems with the fuel you're using.
a.k.a. Charlie Brown
near Syracuse, New York