I'd wouldn't go any further than the KB 2.1 9# intercooled...IF you want the motor to last. And you'd STILL need a very good tune to keep it all together.
I'm running 12 psi on a stock 99gt motor w/ 94K miles. 11:1 GOOD tune and intercooler.
But I saw your going with 4.10's...
Unless you have an auto, that is gunna be OVERKILL! I had 4.10's behind a tr-3650 with 450rwhp and Nitto 555 315's ...1st gear was usless as was second.
I have 3.73's now, first is still useless but second is nice.
Gunna put 3.55's in soon when the turbo goes on.
...and a side note on boost... From what I have seen 12 psi and up comes down to luck more than anything. My friend popped his '04 at 10psi with a great tune and here I am running 12 all day long. So say your prayers and cross your fingers.
Heh, surprised to hear anything but 9psi when talking about KB's.
Just go by their website. the 2.8L is the "competition" blower. that means non-stock internals. Get the 9# 2.1L set up. Then down the road put in a cobra crank and some forged pistons/rods and up the boost to 12#, or sell the small blower and buy the bigger one. Depends on how much money you have.
Also, all my life I've heard that 4.10's are terrible for a blown application. 3.73's are the most popular among the s/c crowd, I believe. If you call/email/research KB, they'll tell you from the testing they've done (and are still doing, btw, on just about every mustang since the 5.0's), with the 4.6L and their blower, 3.73's are the perfect gear for the 1/4 mile. So you might want to rethink the 4.10's when the time comes.
it's no so much boost per se that's the problem, it's how much power you make. you can hit the shortblocks horsepower limit with 8-10psi from pretty much any blower.