If you don't intend on running in the 28+ PSI range, the MMP 1Ks or the GCs may be overkill. You get the benefit from the reduced backpressure at high boost levels. Granted, the MMPs should have the same or better spool, but if you have no intention of boosting that high, why bother. I have regular Stage 3s and am going to get the upgraded manifolds, and I have no "current' plans for PI, but I will likely get a shotgun setup eventually. Given that even stock Stage 3s can pretty much tax a stock block, you have to have a stong will to go all in on the 1Ks, or a hefty budget to use their capability.
I prefer the MMPs as they are stainless steel manifolds and turbine housings vs VTTs cast iron 2.0s. I know the D5S NI resist stuff is popular for turbo OEMS, stainless is offered as an upgrade for most turbo turbine housings, and the finish is much nicer.
While I don't initially intend on 28+, I do like the idea that there is more potential. If I want to build the engine or add more fueling, I can without having to worry about the turbos. I am more and more leaning toward the MMPs.
PS: what outlets are you running?