2.5" vs. 3" exhaust?

[RobbyMartin]

On another message board I raised the question of whether the 2.5" exhaust tube is better for my '02 4.6L over the 3" tube. Opinions were about 60/40 in favor of 3". One guy suggested that the 2.5" provided the proper back pressure and scavenging affect, while others suggesting 3" failed to mention back pressure or scavenging in their opinion.
Now this question becomes even more valueable because I am intending to buy the Gryphon and I'm trying to gather all the info possible in order to have Bill write a tune that is best for my truck. I have a 3" tube installed after the "Y" on my truck, but it was done by an accessory shop, not by an exhaust specialist. Should I have 2.5" put in place of the 3" or should I leave it?
If anyone chiming can also give me opinions on these mods I would appreciate it: I own these already.
Airaid CAI or Gotts mods (I live in So Calif - hot climate)?
Stock or BBK 75mm TB?
U-Drive Pulleys?

I'm more of a daily driver with a heavy foot.