Re: twin turbo and stroker kit
There's a guy on another XR6T forum who is preparing to spend about 12-15K on a rebuild. I think (too lazy to search right now) that he is aiming for 600bhp. That's with a single turbo and no change in computer.
You would need:
* Pistons (seriously doubt cast pistons would cope)
* serious transmission work
* new turbo manifold
* new exhaust/cat etc
* bigger intercooler
.. as well as all the retuning of the car for the two turbos.
Point is, I don't think the limits of the single turbo have been found yet :)