roush uses a t3/t4 I think, which is capable of up 400 I think, it's just a question of whether your exhaust and intake can flow it, and your block can handle it. I think the limit on the standard zetec is around 300 with any reliability. might be less cuz the zetec rods are weak
yeah pretty sure it's a bad idea to have over 250hp on stock internals. but i plan on taking care of all of that beforehand. i'm building up my engine with forged internals, a ford racing head, and thinking about the fr manifold and 70mm tb to go along with it. and a 3" turboback exhaust.