NRM90GT, I've been trying to make the same decision myself. Since I'm building strickly a street driven motor that will probably never see any 1/4 mile action, I want durability without any headaches. And since it's going in an F100, I'm looking for something that has good low rpm power as well as a good increase in the mid range to around 4800rpm. Most of the aluminum heads I considered, had larger valves as well as larger intake ports which would, in my case, make it a little lazy in the lower rpms. This may not be much of an issue in a lighter mustang, but I did'nt want to give up anything in the lower rpms in a truck. Once I get the christmas bills paid, I'll probably get a set of ported thumper e7te heads. They sell for a reasonable price and I don't have to deal with the header issues as with the gt40p's. The flow numbers are quite impressive when compared to some aluminum street heads yet the thumpers still have stock size valves. For my situation, it seems like the best of both worlds, the stock valve size should be good for low rpm torque while the port work should give a good boost in the mid to upper rpms.