Around 550whp is where you start pushing it in terms of reliability. More power can be made, but it's not wise.
What in the world is a "DDS Racing Service T-70"? Are you sure that turbo works well on the Evo and that it's what you want? You can get full Buschur turbo kits (turbo, manifold, dp, etc) for $2995 that are proven to work extremely well. Hopefully, you already have all that figured out.