Honestly at your power level your not going to benefit that much from an aftermarket exhaust manifold. If I were you I would screw the process west tmic and just find a lightly used Sti one and with the money you save from over paying for the process west find a cheap cat less up pipe and Sti injectors as well... Then turn up the boost a bit. Sti intercoolers can handle more power than your stock block can. You can achieve all of this with under a grand if you play your cards right.
Most importantly before adding anymore power make sure the upkeep on the vehicle is up to date. People who chose a new turbo over a timing belt are retarded.