Go for the jugular
If I were Steve Jobs, I'd introduce the proper model we've all seen while being witty and tongue-in-cheek about the leaks. Steve's managed to do that before, especially when his obituary accidentally leaked and "Reports of my death are greatly exaggerated" and it went down a treat with the crowd.
Unveiling a lesser powered model would be seen as capitulating to those who carried out the original leaks and it would also make him look stupid, as well as inciting angry amongst his faithful followers and customers.
I'm seriously considering getting my first iPhone, but if Steve eventually unveils one that's lacking in comparison to the leaked one then I'll probably end up giving it a miss.