Minimize wear & tear on the turbo. Constantly pushing the turbo to it's limit isn't good for it. I have the resources to make the same horsepower out of a turbo with 15psi as I can with a smaller turbo pushing 24psi. Why would I want to strain that poor little turbo so much? That's just setting up for future problems, plus I'd like to be able to push more psi out of my turbo if I really wanted to(such as up the boost when I go to the track).

 

Well it doesnt quite work like that.. the only time you start to really decrece the life of a turbo is when you go over like 25... 20 is perfectly fine. 20 will last almost as long as 15... seriously the difference is miniscule.... although the logic behind it is good... butwith a bigger turbo.. you will be sacrificing a lot of spool time... I think you could make 350 crank hp with about 18ish psi

 

That 18g one looks like a good choice.. And you would have room to grow for taking it to the track.. But that should spool up fast enough for every day driving...

 

But im trying to take into consideration his auto x and stuff. I still think the 16g is more than adiquate.

 

And that is fine, but I wouldn't expect an auto-x car or road car to stay under 2500rpm at anytime unless you are afraid to take it to the stock rev limit or below. Power & spool follow each other in a "window" of operation. Why be worried about having a car that spools just off idle? You'll run out of turbo before you run out of gear.