-7 and -9's won't do the figure you want. What you have at the moment with some boost up its bum will prob crack the 400 mark on E85, other than that it's -5. There are a couple other options out there now. Check out this discussion. http://www.skylinesaustralia.com/forums/topic/445007-the-frankinstien-twin-turbo-thread/
You do NOT need Tomei manifolds. They do a really good job as a door stop or a paper weight and thats about it. I would also suggest ditching those split dump pipes and replacing with bellmouth/open style pipes.
Do you plan on stretching the capacity abit? IE Stroking it? At the end of the day, you're lugging around 1600 KG plus of car with a smallish capacity, short stroke, relatively lowish comp turbo charged engine. It's going to need a few revs whatever the turbo choice.
There is plently of info in the forced induction thread about this. Have a decent search.