take your average duramax... Sleeve the tie rods for a few hundred bucks, spend $5000 on the allison, throw in a lift pump and a couple other minor bolt ons, hit it with EFI live and have a 500+ HP monster.
In perspective, I have about 4-5 grand in upgrades to my truck as it sits. Another $5000 for the turbo and injectors I want will put me at a reliable 500 RWHP. That's close to 10 grand for 500hp and still running through a stock tranny that won't hold forever at that level...
All that being said, I still love my ford, but I can't fault a guy for going with a duramax or a CR cummins. The power is just too easy compared to what we have to deal with. Good luck to the OP, whatever you choose.