I was informed that the 68mm turbine wheel flows more than the 71mm wheel.
At one time, I ran a 66/71/.70 secondary, and I can say that between the 71mm and the now 68mm turbine in a T4 x .83 housing...the 68mm in a T3 x .70 was the most responsive of them all.
I also ran a 66/73/.80...but it's not even in the same spool up catagory....I'm pretty sure the Second Coming is faster then the 73mm turbine wheel in a .80 housing.
........But I would like to see the new 73mm turbine wheel design...