This autospeed article tested stock EB and AU I6 heads;
On the intake side the stock the EB flowed 330hp while the AU was back at 302hp. On the exhaust side the EB was again better than the AU but it doesn't quote hp figures other than to say that exhausts always flow poorer than intakes.
The AU head is considered a better candidate for mods however and is improved from 302hp to 362hp.
See also this thread;