Well your going to see at least 75 hp more LOL! I hope they have a good tuner and dont blow up your motor. Without knowing what turbo they are using it is hard to say what numbers you might see.
I honestly wouldnt want to see much more then 550 on the stock block anyway.
To bad you went with STS as your FI option, because that money plus the 25k you still have could have built a nice option from GTM. Still 25k can go a long way. I would seriously give Sam a call and see what he can do for you with that amount.
I know they have a 700HP package for 30k that inculdes a full turbo kit. Maybe you can get a price without the TT kit, and find out what kind of turbo you need for your current setup to make the right numbers.
Well to be fair some of your posts/threads raise eye brows and I understand why. Aside from that I think your alright so I try to help out without being a d**k.
It will be tough to get 700+ HP on the 3.7 on pump gas. If you look up Mr.Squeez he currently has the highest HP 370z I know of (not counting the white dragon/unicorn). If you fully build this motor like he has it is still hard to reach that number on pump gas.
GTM is very helpful and will always answer/call you back to answer any questions you may have. I hope by the end of next year to be having this same talk with them. As of right now I have not dug to deep into what mods you need for the power levels your seeking besides: Built motor, larger injectors, larger turbos, fuel pressure system, and cooling items, like better CFM fans, and better radiator.