Hey mate, it really depends what you want out of the car. There will always be pros and cons with anything you choose. The external gate is the choose for better control of boost pressure but then you have the cons of purchase price of the gate and the new manifold.

I would suggest that you don't let the workshop decide on what to do as there goals may not be the same as yours. What specs have you built your motor to? No point going for a massive turbo and external gate if you haven't done some head work and added cams.

Do you have you car running and now want to go faster or are you just trying to build it bigger and better before it is even running? I still haven't completed my build but I have been in another 1200 ute which was a standard unopened engine amking aroun 150rwkw running a S15bb turbo, large exhaust, R31 LSD etc and it would spin 1st though to 4th gears on the street. Maybe try and get a ride in a few ca18 power 1200's and then make your decision from there (all assuming yours isn't and hasn't been running).

^^^+1 I only run a gt2535 with a internal wastegate, which a smallish turbo and I can run up to 20psi. I can spin 1-3rd easy on street and still beat most cars on the road. I reckon go t28 or something which would be the cheapest option and still get big power. Also if u have big power in a datto ute it is point less on the street cause ya just spin and slide.