I agree with Outlaw, if 700hp is the goal, than it's not necessary to go to a twin turbo setup. My car was in the June issue of Motor Trend. With the Kenne Bell snout and 2.5" pulley, Accufab throttle body, and an SCT reflash it had 720 hp at the engine.
If you put either an Accufab or Bob Ida Exhaust you can get another 20 whp and some weight savings.
Pretty close to 700hp at the wheels for a fraction of a TT setup. And, as Outlaw said, if you want another 50 whp a small shot of nitrous won't hurt the engine at all and you'll be way above 700.