A ported standard manifold won't make a huge difference now, it's more about individual cylinder flow than just more internal diameter.
The manifolds we're testing have a great flow from each cylinder that prevents back surge or stalling of the turbine wheel, this is where more gains are seen, it just gives more of a torque feel, you'll see more ft-lb gains than bhp but this is what the 20vT engines really needs as they are very flat standard.
I'd agree though, wait till you're swapping turbo if you are, although the turbo is the worse part, the manifold has to come off to swap the turbo ideally so might as well do it all in one go, not twice
