There's a thread on here with ported NPIs and ported PIs and the NPIs out flow the PIs.
Waiting for the New heads to be a bit more reliable before I purchase a set. I currently have the Accufab Plenum and 70MM TB on my Bird and it helped. Buddy with his Mach1 won the TB at a drag race, so I got it pretty cheap.
Remember if you are getting more into it you have to have a way to get that more out of it also. That plenum and TB produce more air then the heads can use.
NA the 75mm wont gain you anything over the 70mm.
Honor, Grace, and Dignity.....Do you remember these?